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MODERN LOCOMOTIVE
ALVES AND VALVE GEARS
By
> r-
HAS. U IVICSHAN
\
I LLXJSXR AXE^ D
Price $2.50
1917
GRIFFIN & WINTERS
New York Life Bldg.
Chicago, HI.
U. S. A.
MODERN LOCOMOTIVE
VALVES AND VALVE GEARS
By
cmAs. l^. ivicshaime:
\
I LLXJSXRAXE^D
Price $2.50
1917
GRIFFIN & WINTERS
New York Life Bldg.
Chicago, HI.
U. S. A.
Copyright, 1917
By Chas. L. McShane.
DEDICATION.
this book is affectionately dedicated to
the memory of my father,
Charles McShane,
WHOSE writings ON MECHANICAL SUBJECTS
assisted so many men, with the hope
that this work may help others
having to do with modern
locomotive valves and
valve gears.
The Author.
329492
PREFACE.
While it is true that there have been many good
books published regarding the subject of valves and
valve gears, it is, however, a regrettable fact that there
is not a book on the market today treating the modern
types from a strictly practical standpoint.
In attempting to supply this deficiency, we have
assumed no knowledge on the part of the reader re-
garding the subject, and, as a result, have devoted
considerable space to elementary, or fundamental princi-
ples, so as to enable the apprentice or student to travel
the road from early to modern practice with ease.
Naturally, some of this information cannot be expected
to be of much interest to the experienced man, but the
author believes that a statement of the general principles,
so compact in form and simple in arrangement that all
herein contained can be thoroughly mastered, and be-
come a part of the mental stock of the reader, will be
interesting and profitable. In fact, the work is presented
with no journalistic pretensions, but special care has
been take to use plain, common sense language, so that
it may be understood by anyone who can read the
English language. But, in the final analysis, the work
must speak for itself — its value must be measured by
the merit its use may develop, its faults could not be
diminished nor excused by anything the author might
here say.
While special efforts have been made to use the
utmost accuracy, it is almost impossible to prepare a
work of this nature entirely free from error, but the
book is presented with a realization of its imperfections.
If the reader will kindly call the publishers' attention to
any errors, of omission or commission, he may find in
the work, correction will be made in future editions, and
the favor will be greatly appreciated.
To enumerate all the sources of information to which
the author is indebted, in connection with the prepar-
ation of this work, would be an almost impossible task,
yet we cannot refrain from publicly acknowledging the
numerous courtesies, and the aid, extended by the
American Locomotive Company and the Baldwin Loco-
motive Works; and to Mr. John J. Lahey, of the C. C.
C. & St. L. Ry. Co., Mattoon, 111., and Mr. Thomas J.
Pembroke, of the Pennsylvania Co., Chicago, 111., for
carefully reading the proofs and for their many valuable
suggestions. To other friends and inventors, we have
privately made due acknowledgment.
C. L. McS.
Chicago, 111.,
November i, 1917.
INTRODUCnON,
In the preparation of this work we have attempted to
confine our discussion to the valve and the valve gear
used on the locomotive, as distinguished from the sta-
tionary engine. Of course, some principles and prac-
tices are common to other types, and may be helpful in
some instances, but where our statements are in conflict
with the approved practice relating to such engines, the
fact should be kept in mind that the following pages are
primarily intended to apply to locomotive construction
and practice only.
It is our desire to make the discussion of the valve, and
the valve gear, as plain as the technical character of the
subject will permit, but the subjects are most important,
and a study of them should not be entered upon, by the
apprentice or student, until he has become thoroughly
familiar with some of the terms used.
With this idea in mind we shall first explain the mean-
ing of the terms and expressions most commonly used in
discussing the valve, and the valve gear, and, later on,
give the reason for their application.
8 MODERN LOCOMOTIVE
This arrangement is somewhat irregular, but it will
serve the two-fold purpose of supplying the reader with
indispensable knowledge, and also dispense with the repe-
tition of such definitions throughout the work.
General Definitians and Technical Terms.
Admission. — ^A word used to describe the entrance of
steam, from the boiler, through the valve chamber to
the cylinder, to be used in moving the piston.
Inside-) Is the term applied when steam from the boiler
is supplied to the center of a piston valve between its
two heads, and is exhausted through the channels at
the end of the cylinder. The point is shown in
Fig. 54.
Outside-) Is just the opposite of m^^-admis^on ; that
is, it commences when the outside edge of a slide valve
reaches the outer edge of the steam port, and the valve
begins to open the port. This point is shown in
Fig. 6.
Point of-) Is the position of the valve when it begins
to uncover the steam port for the admission of steam
to the cylinder.
-Port.) Is a channel, or port, through which steam from
the boiler gains access to the cylinder. See Fig. 2.
Pre-) Is the distance from the front of the advancing
piston to the end of the piston stroke when the valve
VALVES AND VALVE GEARS 9
begins to open for the admission of steam ; the space
the crank must travel to reach the dead center. It
begins when the valve opens the port for lead and ends
when the crank is on center — ^the point where lead
commences. See Fig. lo.
-Valve.) The valve which controls the admission of
steam to the cylinder.
Advance. — (See Angle of Advance, Linear Advance,
etc.)
Angle of Advance. — Represents the distance the center
of the eccentric is advanced toward the crank-pin from
a line drawn through the center of the axle at right
angles to the center line of motion. Or, the com-
bined angle of lap and lead through which the valve
must move from its central position to the position it
should occupy when the crank is on dead center. It is
sometimes designated angular advance and is indicated
by Fig. 17.
Lead-) (See Lead.)
Back-Pressure. — (See Pressure.)
Balanced- Valve. — A slide-vdAwe is said to be balanced
when it is so constructed that the pressure on its top
is just enough in excess of the pressure under it to
insure the valve remaining on its seat under normal
conditions. A piston-vslwe is balanced by allowing
the steam pressure to reach all parts of the central
lO MODERN LOCOMOTIVE
cylindrical form, which moves in a cylindrical cast,
and connects the heads at each end.
Bell-Crank. — Is a rectangular lever by which the direc-
tion of motion is changed through an angle, and by
which its velocity-ratio and range may be altered at
pleasure by making the arms of different lengths.
Bridge. — (See Valve Bridge.)
Bushing. — (See Valve Bushing.)
Center. — That point within a circle which is equally
distant from every point of the circumference.
Dead-) Is that position of the arms of a link-motion in
which the center-lines coincide with the line of effort;
that is, when the links are in the same straight line.
Thus, when the crank, connecting-rod, and piston-rod
are in a straight line, the engine is said to be on its
(front or back) dead center.
Line of-) A straight line joining the centers of two
wheels in gear. The dead line; that line in which a
crank and connecting-rod stand when their axes form
a straight line.
Clearance. — Is the entire space beneath the valve-face
which is filled with steam at the completion or begin-
ning of a stroke, including the space between the piston
and cylinder-head and the volume of the steam chan-
nels to the valve seat.
X'ALVES AND VALVE GEARS II
Exhaust-) Is the distance the exhaust edges of the valve
lack of touching the exhaust edges of the admission
ports when the valve stands central on its seat. It is
sometimes referred to as exhaust-lead.
Inside-) In a slide-valve is not a portion of the valve
proper, but the term represents the space between the
inner or exhaust edge of the valve and the inside
edge of the port opening when the valve stands mid-
way in its travel. See Fig. 5.
Outside-) In a piston-vslvey is the distance from the out-
side edge of the piston ring to the outer edge of the
exhaust port when the valve stands central on its
seat.
Piston-) The distance between the piston and the cylin-
der head at the end of a stroke.
Combination-Lever. — Is a lever which, indirectly, con-
nects the valve rod to the crosshead and removes the
lap of the valve for the admission of steam, by open-
ing the port the desired amount of lead with the begin-
ning of the stroke of the piston, thereby eliminating
the effect of the angularity of the main rod. It is
often referred to as the lap and lead lever, and is shown
in Figs. 75 and 100.
Compression. — Is the term applied to the arrangement
by which the exhaust opening is closed before the
stroke of the piston is ended.
12 MODERN LOCOMOTIVE
Point of-) The point at which compression begins is
reached when the inside, or exhaust edge of the slide-
valve reaches the inner edge of the steam port and com-
pletely closes the steam port and cuts off the exhaust
steam. In other words, compression begins where the
back pressure ends. The point of compression with a
slide valve is shown by the arrow a when the valve
is travelin.s: in the direction of the large arrow A in
Fig. 7, and is shown by the arrow a, in Fig. 55, with
the piston valve.
CoNNECTiNG-RoD. — A link which connects a rotating
crank with a reciprocating rod and converts the re-
ciprocating motion into a circular motion.
Crank. — A crank is a device by which the reciprocating
motion is converted into circular motion, or vice versa,
consisting of a crank-arm, one end of which is fastened
rigidly at right angles to the rotating shaft or axle,
while the other end bears a crank-pin, projecting from
It at right angles and parallel to the shaft. When the
reciprocating part of a machine, as the piston and
cross-head, is linked to this crank by a crank-rod or
connecting-rod, one end of which works on the crank-
pin and the other on a pin at the end of the recipro-
cating part, the to-and-fro motion of the latter imparts
a circular motion to the shaft, and vice versa.
VALVES AND VALVE GEARS 13
-Arm,) Is that part of a crank which joins the center
of the shaft to be turned by it to the handle or pin
to which the power of resistance is applied. See
Fig. IS. '
'Circle, ) The circle described by a crank-pin ; specifically,
the circle in a valve-diagram, or the elevation, of a
steam-engine, which represents the path of the crank.
-End.) The crank end of the cylinder is the end nearest
to the crank shaft, and the farthest from the crank is
the head end.
Leading') Is the crank which leads when the engine
is running ahead. The one which is less than half a
revolution in advance of its fellow pin when the
engine is running ahead.
'Motion,) The motion of a body driving or when driven
by a crank. Such motion is called harmonic, as the
reciprocating part tranverses the diameter of the circle
in the same time in which the crank-pin is moving
uniformly over the semi-circumference of the same
circle.
-Throw.) May be defined as the distance from the
center of the shaft to the center of the crank-pin.
-Web.) Is that part of a crank which connects the crank-
pin to the shaft-hub. In short cranks this may be as
large in cross-motion as either hub, while in long cranks
it is usually cut away to make it as light as possible.
14 MODERN LOCOMOTIVE
-Wrist) The short length which forms the crank-pin
surface to which the connecting-rod is attached.
Crosshead. — Is a bar at the end of the piston-rod of an
engine which slides on ways, or guides, fixed at the bed
of the frame of the engine, which connect the piston-
rod with the connecting-rod, or with a sliding journal-
box in the crosshead itself.
-Guides,) Are the parallel bars between which the cross-
head moves in a right line with the cylinder. They are
sometimes called motion-bars.
Cut-Off. — Is the cutting off, or closing, of the admission
of live steam before the piston has completed its stroke,
which permits the engine to utilize the expansive force
of the imprisoned steam in the cylinder, behind the
piston, after cut-off haii occurred.
Point of-) The point of cut-off is the point of the piston
traverse at which the valve closes to cut-off the ad-
mission of steam to the cylinder. It takes place when
the valve arrives at the same position as for ad-
mission, but is moving in the opposite direction.
Short-) The cut-off is said to be short when the expan-
sion is long. The expansion, or degree of expansion,
is the reciprocal of the cut-off; for instance, if the
cut-off is 3/S of the stroke, the expansion is 5/3, or
the steam has 5/3 the volume which is occupied when
the valve is closed.
VALVES AND VALVE GEARS * IS
--Valve,) (See Expansion Valve.)
Dead-Center. — (See Center.)
Eccentric. — Is a circular disk, keyed to the axle in
such a manner that the center of the disk and the
center of the shaft do not coincide, thus imparting
a rotary into a reciprocating motion. It is essentially
an 'enlarged crank whose throw equals the amount of
the eccentricity of its sheave, and is only used to
avoid the necessity of cutting, or dividing, the crank
shaft. See Fig. 14.
Adjustable-) One which is so constructed that the dis-
tance between the center of figure and the center of
motion can be varied in order to vary the throw of
the rod. This result is secured either by slotting the
disk of the eccentric, or by mounting one eccentric
upon another so that the effective eccentricity may be
the sum of the difference of the eccentricity of each
link, or may have intermediate values.
Angular advance of-) Is the angle between the center
line of the crank of the engine and that joining the
center of motion and center figure of the eccentric.
See Fig. 17.
-Arm,) Is the arm used with outside valve gears in
place of the eccentric employed with inside valve
gears.
l6 MODERN LOCOMOTIVE
Backward') The eccentric which is used when a loco-
motive is moved backward and the valve gear is ad-
justed accordingly.
Exhaust') Is a term which assumes that the eccentric
is fixed on the shaft, so that a constant valve travel,
and fixed points of release and exhaust closure, may
be obtained. .
-Gear.) A term including all the links and other parts
which transmit the motion of an eccentric.
-Rod.) Is the main connecting-link by which the motion
of an eccentric is transmitted to the valve.
-Sheave.) May be defined as the inner portion of the
eccentric, Which rotates with the shaft. Marked AA
in Fig. 14.
-Strap.) Is the band of metal which embraces the circum-
ference of an eccentric, and within which it revolves
The eccentric-rod is attached to it. It is also called
the eccentric-hoop y and is marked BB in Fig. 14.
-Throw.) Is the distance from the center of the shaft
to the center of the eccentric disk. When the slide
valve and the eccentric are connected by a rod the
throw is equal to one-half the travel of the valve,
or the lap plus the amount of opening of the steam
port for the admission of steam. The distance between
the letters C D in Fig 14.
VALVES AND VALVE GEARS 17
Eccentricity. — Of an eccentric, is the distance between
the center of the shaft and the center of the eccentric,
which is shown by the distance between the letters
C and D in Fig. 14.
Exhaust. — Is the release, or discharge, of expanded
steam from the cylinder.
-Cavity,) Is designed to allow the escape of steam to
the atmosphere, and, in the slide-valve, may be desig-
nated as the space between the exhaust edges. With
the piston valve, however, the exhaust steam passes
through the steam chest, around the outer ends of the
valve, to the atmosphere.
-Clearance,) (See Qearance.)
-Lap,) The amount by which the edges of the working
face of the valve project over the exhaust edges of
the ports when the valve stands in its central position,
symmetrical with the ports. See Fig. 4.
-Lead.) The amount by which the exhaust-port is open
for the exhaust of steam, before the end of the pres-
sure-stroke, or the commencement of the return stroke.
-Nozzle.) Is the blast-nozzle, or -orifice, which dis-
charges the exhaust-steam into the stack to make a
forced draft.
-Port) Is the opening, or cavity, in the valve seat in
which the exhaust passage terminates. See Fig. 2.
l8 MODERN LOCOMOTIVE
Point of') That point in the stroke of the piston at
which the valve opens to release from the cylinder the
steam which has performed its work in driving the
piston.
Expansion. — Is the increase in volume with corre-
sponding reduction in pressure which occurs in a
cylinder when the steam supply is cut off between the
boiler and the cylinder, while the piston continues
its motion.
Initial-) The expansion of water into steam which oc-
curs in a boiler when the valve is opened to supply
steam to the engine-cylinder. It is an amount suffi-
cient to fill the cylinder and its clearance-volume up
to the point at which cut-off takes place.
-Valve,) A valve, or slide, on the back of the main
slide-valve for cutting off the steam earlier and more
sharply than is done by the main slide-valve, thus
causing a greater degree of expansive work of the
steam than could be secured by the use of the main
slide-valve alone.
Variable-) A term employed to designate expansion
which varies under different conditions. It may be
secured by changing the point of cut-off at will while
the engine is at work, it may be fixed or secured at
some pre-determined point of the stroke, or it may
be automatic or self-varying.
VALVISS AND VALVfi CEAkS 10
Gear. — ^Those parts of a machine which are concerned
in effecting motion, as, for example, the parts of a
locomotive from the cylinder to the wheels inclusive.
Full') Such an arrangement of the valve gear mechan-
ism as will give the longest period for the admission
of steam.
Full-backward') With the valve-gearing adjusted to
produce backward motion of the engine.
Full-forward') With the valve-gearing adjusted to pro-
duce forward motion of the engine.
Lap. — The amount that the valve extends over the steam
port when the valve is in its central, or mid-position,
or the space traveled by a valve after closing the
steam port to or from the cylinder before reaching
its central, or mid-position.
Amount of-) The lap is always measured at one end
(not both) of the valve when it is in mid-position.
Effect of') Is the cutting off of the admission of steam
before the piston reaches the end of its stroke.
Exhaust') Is that part of the valve which overlaps the
steam ports when the valve stands in its central, or
mid-position. It is sometimes referred to as outside
and inside lap, and, occasionally termed positive ex-
haust lap because it represents metal added to the ele-
mentary valve, but the term exhaust lap is more pref-
20 MODERN LOCOMOTIVE
erable, because it refers to the outside when a piston-
valve is used, and the inside for a slide-vBlvt.
Inside-) The inside lap of a slide-waive is the amount
by which each of the exhaust edges of the valve over-
lap the inside edges of the steam port when the valve
is in its central, or mid-position. It is also called
exhaust-lap, or cover, and is shown by the space be-
tween the lines D and E in Fig. 4.
Negative-) The amount by which the exhaust edge of
the slide-yalye^ when it is in its central, or mid-
position, falls short of reaching the inner edges of
the steam ports; the uncovered part is termed nega^
tive-exhaust lap, negative-lap or inside-clearance, and
is shown by the letters C and C in Fig. 5.
Outside-) Is that part of the valve flange which over-
laps the steam port, when the valve stands central
upon its seat. It is also called steanu-lap, or simply
lap, and is shown by the space between the letters A
and B in Fig. 4.
Seal-) (See Seal.)
Steam-) The distance the valve is moved from its cen-
tral position to permit admission or cut-off to occur.
See outsi de-lap.
Lap & Lead Lever. — (See Combination Lever.)
Lead. — ^The distance, or width of port opening, for the
admission of steam when the crank is on dead center.
VALVES AND VALV£ CEARS 41
-Angle,) Is the angular displacement of the center line
of the eccentric ahead of its normal relation to the
center line of the crank, which is given so that the
opening of the port may precede or lead the beginning
of the piston stroke by a predetermined amount. The
point is shown in Fig. 17.
Constant') Implies a uniform lead, which does not
change for varying grades of expansion.
Equal") Means an equality of, or the same amount of
lead at both ends of the cylinder.
Exhaust") The lead on the exhaust side of the steam
port. (See Exhaust-lead.)
Negative-) A term used to designate the distance which
a valve has to travel, at the beginning of the stroke,
before it opens the port. Or the angle through which
the crank has turned from the dead center when the
valve opens to admit steam. It indicates the amount
the steam-edge of a valve overlaps the steam-port at
the commencement of the stroke.
Positive-) The amount, or distance, the valve has opened
the port before the piston commences its stroke.
Steam-) The lead on the steam-side, or at the ad-
mission port.
Variable-) Is the opposite of constant-lead. It is lead
which varies, or is liable to change, for varying grades
of expansion.
22 MODERN LOCOMOTIVE
Ijnear-advance. — ^The distance the valve is moved
from its central, or mid-position when the piston
reaches the end of its stroke. Or the distance by
which the port is open when the piston begins its
stroke.
Link. — Is a bar in which there is a slot, and the latter
may be straight or may be a curve of large radius.
The adjustment of the link block in the link deter-
mines the motion or direction of the locomotive, as
well as the travel of the valve.
-Block,) The block attached to the valve-stem, actu-
ated by the link-motion.
-Carrier.) A metal piece which carries the link in a
locomotive valve gear; a stirrup,
-Foot,) Is the extension of the link used in the Wal-
schaert gear to which the eccentric rod is connected.
-Hanger.) Is the suspension-rod fastened to the saddle-
pin in the Stephenson link-motion valve gear, by
which the weight of the link and of the eccentric-rods
is borne, and by which the link is raised and lowered.
Main-) The link that connects the end of the radius
bar on a steam-engine to the valve-stem.
-Motion.) A system of gearing for controlling the
valves, for the purpose of starting or reversing the
engine, and for controlling the cut-off.
Oscillating-) (See Oscillating.)
VALVES AND VALVE GEARS 23
Radius of the-) Is the distance from the center of the
main shaft to the center of the rocker box, minus any
backset given the rocker arm. It equals the exact
length of the eccentric blades, plus the distance from
the link pin arc to the link arc. On outside radial
gears, it is the length of the radius rod, or the distance
from the valve-stem connection to the center of the
link carrier.
-Saddle,) The plate, or bar, bolted to the side of the
link, and to which the link-hanger is attached.
-Saddle-stud.) The pin, or extension, on the saddle, to
hold the link hanger in position.
Slip of the-) Is the distance that the link-block moves
up and down in the link while in motion, without any
movement of the reverse lever.
-Slot,) The slot, or opening, in the curved member of a
link-motion for a locomotive and other reversing en-
gines. This member is called the link, and in the
opening, or slot, slides the link-block by which the
valve is operated, as the two eccentrics operate the
link itself.
-Stirrup.) (See Link-carrier.)
-Swing,) The greatest distance that the bottom of the
link will swing from front to back in full gear.
24 MODERN LOCOMOTIVE
Union-) A bar or link which connects the lower end of
the combination lever with the crosshead; also called
the lap and lead connector. See Fig. 102.
LiNKiNG-UP. — ^The act or process of altering the posi-
tion of the links or link-blocks in a reversing and cut-
off engine, to produce an earlier cut-off and greater
expansion. Also called hooking-up.
Lost-motion. — Any difference of motion between the
driving parts, or between the parts of a locomotive,
or any machine.
MAiN-/>m. — The crank pin to which is connected the
back end of the main rod.
-Rod,) The rod that connects the crosshead to the main
pin.
Motion. — Is the movement from one point or position
in space to another.
Center line of-) By "the center line of motion of the
valve gear," is meant a line drawn through the center
of the shaft parallel to the direction in which the valve
moves, when no rocker, or other mechanism between
the shaft and valve, is used.
Direct') A valve gear is said to be a direct motion one
when any movement of the eccentric or eccentric rod
causes the valve to move in the same direction. A
forward movement of the eccentric will thus push
the valve forward.
VALVES AND VALVE GEARS 2$
Indirect-) A valve is said to be indirect when a for-
ward movement of the eccentric causes the valve to
move back.
Lateral-) Is the end-play, or freedom of movement, of
an axle in its boxes.
Link-) (See Link-motion.)
Lost-) (See Lost-motion.)
Reciprocating-) A motion of a part out and back over
the same path, first in one direction and then in the
other; also the parts which have such back and forth
motion.
Reverse-) (See Reverse-motion.)
-Rod,) The rod which communicates motion from a
rock-shaft, driven by the eccentric, to the valve-stem.
Also called a transmission-bar.
Valve-) Is the motion transmitted to the valve by the
valve gear. In other words it is the travel of the
valve.
Over-Travel. — ^The distance a valve travels beyond the
point necessary to give a full steam port opening. See
Fig. 8.
Oscillating. — ^Anything which moves backward and for-
ward, or swings to and fro ; a link on a block.
PiSTON-^r^a.) The area of the flat surface or end of
the piston; the area of the cross-section of the bore
of the cylinder.
26 MODERN LOCOMOTIVE
-Clearance.) (See Clearance.)
-Displacement.) The distance the piston has traveled
from the end of its stroke. The volume of a cylinder
having the same diameter as the piston and a length
equal to its stroke.
-Head.) The disk which is fitted closely to the interior
of the cylinder, and is the direct receiver or transmitter
of the power developed ; distinguished from the piston-
rod.
-Rod.) The rod that connects the piston head to the
crosshead, which, in turn, is connected to the main
pin by the main rod.
-Stroke,) A stroke of the piston is equal to the diameter
or the circle described by the crank-pin. The distance
of its travel from one end of the cylinder to the other.
-Travel.) (See Piston-stroke.)
-Valve.) Is a slide valve of cylinder form, or a spool
shaped device, which moves in the direction of its
axis. It is hollowed in its center and fitted with pack-
ing rings in suitable grooves at each end, to insure
a steam tight joint between the live and exhaust steam
passages.
FoRT-Opening.) The extreme uncovered distance of the
port between the steam edge of the valve and the
steam edge of the port. See Fig. 2.
Pre- Admission.— (See Admission.)
VALVES AND VALVE GEARS 2/
Pressure. — Absolute-) Is the pressure reckoned from
a vacuum; the pressure shown by the steam gauge,
plus the pressure of the atmosphere.
Boiler-) The pressure above atmospheric pressure; the
pressure in a boiler shown by a steam guage.
Back-) Is the pressure on the exhaust side of the piston,
caused by the steam left in the cylinder after the
exhaust opens, which opposes the advancing motion
of the piston during its return stroke, and causes a
reduction of the work to be done by the piston through
the action of live steam.
Effective-) The unbalanced pressure on a piston; the
net pressure available for doing work; the absolute
pressure on the pressure side of the piston minus the
back pressure on the exhaust side of the piston; usually
called mean effective pressure.
High-) Formerly, a phrase denoting all steam engines
working at pressure materially higher than atmospheric
pressure, but now a relative term.
Initial-) The pressure in the cylinder at the beginning
of the forward stroke.
Low-) The precise signification of the term is unde-
termined, but the standard of pressure is steadily rising,
so that engines that were formerly considered high-
pressure are now looked upon as low-pressure engines.
28 MODERN LOCOMOTIVE
Mean-) The average pressure in the cylinder from the
beginning to the end of a stroke. See Effective-
pressure.
-Plate.) A cover-plate attached to the inner cover of
the steam chest, designed to relieve a slide valve of
friction by preventing the steam pressure from coming
into contact with a portion of the upper surface, or
top, of the sliding valve.
Terminal-) The pressure of the steam in the cylinder
at the end of the stroke, or the pressure it would have
if the exhaust port was not opened until the end of
the stroke.
Quadrant. — A link, with a slot struck with an arc of
a circle as center-line, used in the operation of valve
gears, in which the lock or latch of the reverse lever
can be engaged to hold the lever in the desired position.
Called also a valve-sector.
Radius-Bar. — One of a pair of rods pivoted at one end
and connected at the other with some concentrically
moving part which is necessary to keep at a definite
distance from the pivot or center. Also called a radius-
rod.
-Link.) (See Link-radius.)
Reach-Rod. — A rod which connects the reverse lever
in the cab to the bell crank on the reverse shaft of
the valve gear.
VALVES AND VALVE GEARS 2g
Reciprocating-Motion. — (See Motion.)
Release. — ^The opening of a port for the escape of steam
which has been confined behind the piston to drive it
through its working stroke.
Point of') The place in the stroke of the piston at which
the exhaust valve opens, releasing the steam which has
been confined behind the piston. See Fig. 7.
Reverse. — ^To cause to act in a contrary direction; to
give an exactly opposite motion or action to the crank,
or to that part to which the piston-rod is attached.
-Lever.) A lever which operates the valve gear and
the valve so as to reverse the action of the steam on
the piston and thus change the direction of motion.
-Link.) The link or guide in which the link-block of a
reversing valve gear slides.
-Motion.) Any mechanism for changing the direction of
an engine. A common device used is a loose eccentric
working between straps on the engine-shaft, so that it
may be made at will to assume an angular relation to
the engine crank, which shall be correct for forward
or for backward motion.
-Shaft,) A shaft connected with the valves of an engine
in such a manner as to permit a reversal of the direc-
tion of the motion of the engine-shaft.
-Valve,) The valve of a reversing-cylinder. It may be
a plain, slide or reversing type.
30 MODERN LOCOMOTIVE
-Yoke,) A part used in the Baker valve gear to displace
the link, and to reverse the motion of the engine.
Rocker-Arm. — An arm or lever attached to a rock-shaft
so that it may receive or give a reciprocating angular
motion. It changes the motion of the Stephenson gear
from direct to indirect.
-Bar,) A bar or lever mounted on a shaft which has an
oscillating motion.
-Box.) The box or bearing for a rock-shaft.
Saddle- Pin. — The pin which is fastened to the U shaped
forging, and on which the link is suspended by its
hanger.
-Stud,) (See Saddle-pin.)
Seal. — The amount a valve overlaps the edge of a port
to seal it, and prevent leakage, when the valve is in a
closed position for the particular port.
Stuffing-Box. — A box cast around the hole through
which the piston rod passes, in which is laid, around
the rod, and in contact with it, a quantity of hemp or
metallic packing. The packing is lubricated with oily
matter, and a gland or flanged cylinder is placed on the
top of it which is pressed down by screws, so as to
squeeze the packing into every crevice. It is also called
the packing-box,
Transmission-Bar. — A bar of steel or iron used to con-
nect the link block to the rocker arm, or valve rod
VALVES AND VALVE GEARS 31
connection, on an engine where the rocker is placed
ahead of the link. Also called a motion-rod.
Travel. — ( See Valve-travel. )
Tumbling-Shaft. — ^The tranverse shaft in a Stephenson
reversing link-motion from arms of which the link
proper is suspended or controlled in position. When
the engine is horizontal, the arms have a rocking or
tumbling motion through the necessary angle to move
the link from the position from full forward gear to
full backward gear.
Valve. —
Admission-) (See Admission- valve.)
Balanced-) (See Balanced- valve.)
-Block.) A moving block, such as a link-block or cross-
head, used to connect two moving parts.
-Bridge.) The wall, or partition, which separates the
steam-ports from the exhaust cavity. See Fig. 2.
-Bushing.) A cylindrical lining, or form, pressed into
the steam chest, in which the piston valve operates.
-Chest.) The box, or casing, inclosing the valve.
-Clearance.) (See Qearance.)
Cut-off-) (See Cut-off.)
-Displacement.) The amount a valve is moved to the
right or left from its mid-position.
32 MODERN IX)COMOTIVE
-Face.) The finished surface of the valve, on which it
slides, or moves, and fits to open and close the passages
it is to control.
-Gear.) A collective term used to designate the entire
mechanism, composed of the parts from the cylinder
to the wheels, employed to communicate motiofi from
the wheels to the valve.
'Line and line.) A valve is said to be set line-and-line
when it has no lead in full forward gear. That is,
when the line of the edge of the valve coincides with
the line of the edge of the steam port at the beginning
of the stroke. See Fig. i.
Mid-position of-) The position of the valve when the
eccentric is perpendicular to the line of stroke; the
middle of the travel when a valve covers both steam
ports the same amount.
-Motion,) (See Motion.)
-Over-travel) (See Over-travel.)
Piston-) (See Piston- valve.)
-Plate.) A flat plate forming part of the seat of a valve,
which can be renewed upon wearing, or in case of
leakage, without discarding or refinishing the entire
casting.
-Port,) One of the openings which terminate in the
valve-seat, by which the passageways to the cylinder
are placed in communication with the steam pressure;
VALVES AND VALVE GEARS 33
it also serves as a terminal for the discharge of. ex-
haust steam from the cylinder. See Fig. 2.
-Port'Opening.) Is the uncovered part of the port, and
it is generally less than the steam-port width.
-Rod,) The rod which communicates motion from the
rockshaft, driven by the eccentric, to the valve-stem.
Seal.) (See Seal.)
-Seat.) The surface upon which the valve rests and
slides. See Fig. 2.
-Sector.) (See Quadrant.)
Slide-) A slide-valve is one which slides to and fro,
over and upon its seat, partially or wholly opening
and closing a port or ports formed in the valve seat,
which are to be alternately opened and closed for the
admission and exhaust of steam to and from the cyl-
inder.
Stem.) A rod, similar to a piston-rod, by which a valve
is moved.
Stem-guide.) A hollow bar, or stud of iron, in which
the valve stem travels, placed in line with the steam
chest to insure a straight travel of the valve stem.
Spindle.) The stem, or axis, on which a valve is
fastened, and which transmits motion from outside
of the steam, or valve, chest to the valve proper, with-
in it. The spindle, or stem, slides in and out through
a stuffing-box.
34 MODERN LOCOMOTIVE
-Strip.) A straight piece of metal acting as the valve-
ring and used on rectangular balanced valves instead
of a ring, to serve as a packing-strip between the
valve and the pressure-plate.
-Travel,) The linear distance the valve travels in mov-
ing from one extreme position to the other. Twice
the eccentricitv, or throw of the eccentric.
-Yoke,) The loop of metal, or band, around a slide-
valve, which connects the valve to the valve stem.
Wiredraw. — ^Wiredrawing means reducing the area
through which the steam may flow, thus materially
reducing its pressure after passage through the con-
stricted opening.
Assuming now that the 'reader has studied, and is
familiar with, the various terms defined, we shall pro-
ceed to describe the construction and application of the
valve, and, later on, the different types of modem valve
gear.
THE SLIDE VALVE.
There are but two general types of slide-valve — the
Hat valve and the circular piston valve, but each type,
is represented by many different styles, which may be
divided into two classes: direct and indirect valves. A
valve is said to be direct when it moves to the left and
opens the right-hand port, and closes the same when
moving to the right, and is classed as indirect when it
moves to the right to open the right-hand port and
travels to the left to close it. The flat D slide-valve is
an example of the direct type, while the piston valve is
usually of the type classed as indirect.
The oldest, and simplest, form now in use is the flat D
shaped slide-valve, so it will be considered first.
luventioiL
A crude form of the slide-valve, which is shown in
Fig. I, was first used near the end of the eighteenth
century, and Mr. Matthew Murray, of Leeds, England,
is generally accredited as the inventor. The form of
this valve was later improved upon by Mr. James Watt,
36
MODERN LOCOMOTIVE
but the invention of the long D slide-valve, which, in
a modified form, is used at present, is a product of one
Murdock, who was an assistant of Watt.
The plain D slide-valve was simple of construction
and durable, but the efficiency of some of its modifica-
FlG. I.
tions, as, for instance, the balanced slide valve, has
been questioned, and it has formed the basis of severe,
if not continuous, criticism, but it still occupies a prom-
inent place in modern locomotive construction.
Frmctiaiis.
The efficient and economical operation of a steam
valve requires that a certain amount of steam, ample
VALVES AND VALVE GEARS 37
for the load to be moved, must be allowed to enter and
escape from the cylinder at fixed predetermined points
of the piston travel; for example:
First. Steam must not be admitted at both ends of the
cylinder at the same time;
Second. The exhaust of steam 'from the cylinder
should commence a little before, but never later than,
the admission of steam at the opposite end, and
Third. The outer edges of the steam ports should
be covered completely when the valve stands in its cen-
tral position, so as to prevent steam from passing from
the steam chest into the exhaust port.
A valve which will not fulfill these requirements can-
not be used with success or economy.
Satisfactory results can only be obtained from a prop-
erly constructed valve, and its size is governed solely
by the proportions of the valve seat, on which it slides.
For this reason, to assist the reader in understanding
the design of the valves now in use, we present a gen-
eral outline of the valve seat.
Construction of the Valve Seat.
The valve seat is, generally, cast on top of the cylin-
der, and it must be planed perfectly smooth, to avoid as
much friction as possible, and to insure a steam tight
fit. It is provided with two steam channels, or ports —
one in each end, which also serve as exhaust passages;
38 MODERN LOCOMOTIVE
and one exhaust cavity, or port, situated in the center
between the two end ports, all of which terminate in
the smooth flat surface called the valve seat, or base.
Fig. 2.
Fig. 2 shows a top view, and a cross-section, of the
valve seat. The steam ports communicate with the
boiler and the exhaust cavity and port, alternately, while
the exhaust cavity and port terminate with the atmos-
phere, through the exhaust nozzle and stack, for the
discharge of steam which has been used.
VALVES AND VALVE GEARS 39
To insure good service, both the valve and the valve
seat should be made of hard cast iron. It occasionally
happens, however, that the cylinder casting is made of
softer metal than it should be, and, as a result, the
valve seat wears rapidly. In such cases a false seat
must be applied, just as is done when the valve seat is
faced down to its limit. The practice of substituting
false seats should be avoided when possible, for they
are expensive, and are almost sure to give trouble unless
the work is performed in the best possible manner.
The valve seat should always be raised a little, from
I J^ to I ^ of an inch, above the surrounding metal of
the cylinder and should be a trifle shorter than the ex-
treme travel of the valve, to prevent the wearing of a
shoulder on the valve seat.
The longitudinal width of the valve seat is not so
important, except where special valves of the Allen type
are used, but when possible it should be made wide
enough to allow a surface for the valve equivalent to
the width of one bridge when the valve is at extreme
travel position, as hereafter shown in Fig. 8, unless such
allowance would result in the wearing of a shoulder on
• the valve seat when the engine is hooked-up in the work-
ing notch.
40 MODERN LOCOMOTIVE
Bridges.
The bridges should be made as thin as possible, to
reduce the pressure required to move the valve, but of
sufficient strength to resist the highest pressure. The
thickness of the cylinder walls is generally considered
a safe measurement for that of the bridges. They are,
however, usually made a little wider, but the face may
be beveled without materially affecting its strength ; how-
ever, it should be remembered that a reduction of J^
inch in its width will reduce the width of the valve %
inch, and result in a decrease of the area on top.
Over-travel should also be considered, and sufficient
surface be provided for the valve when it is in extreme
travel, position to secure a steam, tight joint, about J4
inch being sufficient. The wear must also be taken
into consideration, for too narrow a bridge would not
maintain a steam tight joint.
As a general rule the width of the bridge is less than
the width of the steam port, and on American loco-
motives it varies from 15/16 to 134 inches.
Part Opening.
An important task in designing a valve is to provide
proper port areas for the admission and exhaust of
steam. If the cross-sectional areas of the port are too
VALVES AND VALVE GEARS 4I
small, the steam will be choked, or throttled, its velocity
increased, and its pressure reduced. This result is gen-
erally referred to as zvire drawing, the effect of which
will be considered later on. On the other hand, if too
large a channel be provided the clearance volume will
be unnecessarily increased, and economy of the* engine
reduced proportionally.
The proper size is that which will insure the largest
port opening practicable at the running cut-offs, while
reducing the preadmission in full gear to a negligible
quantity. Any port opening desired at the working
cut-off may be secured by giving the necessary lead
to the valves. But to reduce preadmission, and render
it negligible, so far as starting is concerned, lap should
be added.. The more lap given a valve the less faulty
steam distribution is to be expected, and vice versa.
Even though changes in speed may not affect the ex-
tent of port opening, the length of time of its opening
will be reduced as the speed is increased, and, as a re-
sult, a smaller amount of steam will be admitted per
stroke, depending, of course, upon the amount the speed
is increased.
In some cases the throttling of steam is unavoidable,
but it can be diminished by a quick opening and closing
of the valve.
42 MODERN LOCOMOTIVE
Location of Port Openings.
It is advisable, when possible, to use a small valve,
and place the ports as close together as practicable, for
friction and weight are important considerations, and
considerable work is required to accelerate and retard
the moving masses employed; besides, the wear and
tear of the valve gear will be in proportion to the act-
ing forces. The unbalanced D slide-valve, as will be
hereafter shown, has steam pressure over its entire back,
or top, and the friction and weight are necessarily in-
creased in proportion to its size.
Steam Ports.
No general rule governing the size of the steam
ports can be stated, for considerable difference of opin-
ion exists in regard to this, and it has not been deter-
mined with any degree of accuracy. But it may be said
the size depends, to a considerable extent, upon the
speed of the piston and the dimensions of the cylinder.
When the admission of full boilef pressure steam to
the cylinder is desired, for high-speed engines, large
ports are necessary, to secure the free admission and
release, but small ports are more satisfactory and pref-
erable, when they can be used, for they keep the valve
motion within practical" limits.
VALVES AND VALVE GEARS 43
The admission of live steam does not require as large
a port opening as is necessary for the exhaust of the
expended steam, and if the port is large enough for the
exhaust to pass out without appreciable back pressure
it will be ample for the admission of steam. In high-
speed engines there is seldom any difficulty experienced
in getting steam into the cylinder, but occasionally trou-
ble is encountered in getting the steam out of the
cylinder fast enough.
It has been demonstrated that for a piston speed of
600 feet per minute, a good exhaust will be secured
when the area of the steam port is i/io the area of the
piston, if the steam is in an ordinary state of dryness.
Of course, for slower piston speeds the steam port area
will be less, and will be proportionally larger for in-
creased piston speed ; in fact the rule of proportion may
be stated as follows:
Given piston speed in feet per minute X .1 -^ 600 =
the port area in fractional parts of the piston area.
In other words, the specified piston speed in feet per
minute multiplied by i/io, and divided by 600, will
equal the port area in fractional parts of the piston area.
Now, if we multiply the area in square inches of the
piston by the port area, in terms of the piston area, we
can ascertain the number of square inches that the steam
port must contain; for example:
44 MODERN LOCOMOTIVE
To find the steam port area for a cylinder 24 inches
in diameter, and a piston speed of 650 feet per minute,
we may put our data in the following form:
650X.1
=.108
600
that is, the port area must be equal to 108/1000 part
of the piston area. The area of a piston 24 inches in
diameter is 452,39 square inches, hence 452.39X.io8=
48.85812. This means that the steam port must be
48.85 square inches for this particular piston speed. Of
course, for a slower piston speed, this port area should
be less, for instance, if the piston speed is to be 500
feet per minute, and the diameter of the cylinder 24
inches, as in the previous example, we have —
500X.1
=.083
600
and the piston area 452.39X. 083=37.4837 square inches
for port area.
To ascertain the proper area for a steam port it is
only necessary to multiply the area of the piston in
square inches by the number opposite the piston speed
shown in the following table, which has been found to
give good results :
VALVES AND VALVE GEARS 45
Speed of piston in
feet per minute. Multiplied by
lOO ' oi6
150 025
200 033
250 041
300 050
350 058
400 066
450 .075
500 ' .083
550 091
600 100
650 108
700 .* 116
750 125
800 133
850 141
900 150
950 158
1000 166
Another rule for ascertaining the area of the steam
port is this; multiply the square of the diameter of the
cylinder by .078.
The length of the steam port is usually made equal
to, but should never be less than three-fourths of, the
46 MODERN LOCOMOTIVE
diameter of the cylinder. Better results are obtained
from a long port, as it increases the opening for admis-
sion and release, reduces the travel necessary to obtain
a full port opening, and reduces the area on the back of
the valve, so that the valve can be moved with less
power.
Assuming that the length of a steam port, with square
ends, has been decided upon, the necessary width of the
port can be ascertained by dividing the area of the steam
port by its length. If predetermined width is specified,
divide the area of the port with the width, and the
quotient will be the length of the port.
It is a general rule, in practice, to make the port
opening coincide with the passage, or channel. It is
also considered good practice to have the ends of the
steam ports form a semi-circle, as shown by the dotted
line at the end of the ports in Fig. 2, for ports -with
square ends are liable to wear grooves and ridges, al-
though they admit and cut off steam along the entire
edge of the part at the same moment. Another ad-
vantage derived from constructing the ends of the ports
semi-circular is the additional strength given to the
bridges.
Exhaust Port.
The exhaust port should be made more than twice
the width of the steam port, especially with over-travel,
VALVES AND VALVE GEARS 47
to secure the free escape of steam and reduce the back
pressure as far as practicable; if made smaller it would
throttle or choke the valve, as shown by Fig. 8. On
the other hand, it should not be made too wide, or it
would unnecessarily add to the size of the valve and
increase the pressure on it, thereby increasing friction
and the wear and tear on the valve gear. In addition,
it may be noted here that the size of the exhaust port has
no material influence on the valve. With unbalanced
valves, however, it is considered good practice to re-
duce the exhaust cavity as much as possible; in such
a case the exhaust cavity opening at the extreme end
of the valve travel may be reduced to about five-eighths
of the width of the steam port area, as a result of the
valve overlapping.
The general rule for ascertaining the width of the
exhaust port may be stated as follows: Add the width
of one steam port to one-half the travel of the valve,
and from that amount subtract the width of one bridge.
Another rule for determining the area of the exhaust
port, is to multiply the square of the diameter of the
cylinder by .178.
Assuming now that the reader has a general idea of
the form of the valve seat, the question arises : What size
shall we make the valve?
48
MODERN LOCOMOTIVE
Consti-uction of the Valve.
We do not believe an analysis of the various theories
advanced in favor of a large or small sized valve would
j2_
Fig. 3.
be of any benefit to the reader at this time ; therefore, we
shall proceed to construct a valve for the valve seat pre-
viously illustrated.
The face of the valve seat is here shown by the line
A B in Fig. 3, and we will now draw the perpendicular
line C D through the center of the line A B to locate the
VALVES AND VALVE GEARS 49
center of the exhaust port and the center of the valve
when it stands in mid-position.
If the valve be constructed without inside lap, or in-
side clearance, its inner edges must coincide with the
inner edges of the steam ports, and its inside width must
equal that of both bridges and the exhaust port, or be
ij4+iM+3=Sj^ inches.
Next we will draw the heavy base lines from the outer
edges of the bridges to the outer edges of the steam
ports, a distance of i^ inches.
This will give us a valve which is termed line and line,
as shown in Fig. i, but such a valve would not be satis-
factory, for reasons we shall soon make clear ; therefore,
we must give the valve lap, and, without stopping at this
time to state the rule for determining the proper amount
of lap for any particular valve, we will add the width of
one bridge, or ij^ inches, at each end; so that our heavy
base line is now ij4+^H=2H inches.
Now in determining the thickness of the metal neces-
sary to support the valve face we must allow something
for wear, and its depth should be enough to insure a
proper support for the valve yoke, so we will make the
flange twice the thickness of the sides or top of the
valve, or say i inch.
Now, to lay out the exhaust cavity, we will draw two
heavy lines i inch high, to correspond with the outer
50 MODERN LOCOMOTIVE
edges of the valve flanges, from the inner edges of the
steam ports, making the two lines perpendicular to the
line A B. The depth of the exhaust cavity is sometimes
made a trifle less, but it should not be greater, than the
width of the exhaust port plus one steam port. We be-
lieve, however, the larger size will give better results so
we will make it 3+1^=4^ inches.
Now we must decide upon the height of the outer walls
of the valve, and upon the shape of the top of the valve,
for some valves are constructed with a round top, as illus-
trated in Fig. I, while others are made with a square top.
If the flange of a valve face is allowed J/$ inch for
wear, then the thickness of the top and sides for either
form of valve may be made the same, for they do not
come in contact with a wearing surface, and are not sub-
ject to wear.
Without attempting to decide the advantages to be de-
rived from the adoption of either form of top, or crown,
we shall assume the round top is, for some reason, un-
desirable.
Now returning to Fig. 3, we will draw a light line,
from the top of the outer end of the metal flange sup-
porting the valve face, to a point J^ inch from the inner
edge of the exhaust arch.
It is now obvious the outer sides designated E F and
G H must extend upward a distance in excess of the
VALVES AND VALVE GEARS S^
depth of the exhaust cavity (4^ inches), and the thick-
ness of the exhaust arch {y2 inch), or a total of 4%
inches to secure a square top, so we will draw the two
outer lines to a point 5 inches from the valve face.
The two depressions, or recesses, indicated by the let-
ters L M are solely for the purpose of saving metal and
dispensing with unnecessary weight of the valve.
A flat top for the valve is preferable because the in-
creased height of the valve provides a larger surface
against which the valve yoke may bear, and it gives a
form which may be laid on its back and secured to the
planer without difficulty, when the valve face is to be
planed. The flat top also furnishes a convenient base for
the insertion of balance springs and strips when it is
desired to convert a plain slide valve into a balanced
valve.
Valves Without Lap.
By referring to Fig. i again the reader will observe
that the valve is in a position described as line and line;
that is, as previously explained, the inside and outside
edges of the ports and the inside and outside edges of
the valve coincide; by moving this valve in the slightest
degree, either to the right or left, steam will be admitted
in one port, and, at the same time, the opposite port will
be opened to the exhaust of steam. Thus, the duration
of steam admission at one end would be the same as
52 MODERN LOCOMOTIVE
that of exhaust at the opposite end of the cylinder. A
valve of this kind would admit steam to the cylinder
during the whole stroke of the piston and be extremely
wasteful, because it would not use the expansive power
of the steam.
Such a valve is generally modified so the admissicm of
steam will be cut off before the piston reaches the end
of its stroke, so as to obtain the advantage of expansion.
It has also been demonstrated that, among other ad-
vantages, a considerable saving in coal can be obtained
by permitting the admission of steam for only a part
of the stroke and allowing the steam in the cylinder to
expand for the remainder of the stroke.
Valves without lap are not in use at the present time,
however, and the illustration is beneficial only in showing
the development in valve construction.
Valves With I.ap.
The valve was given lap in this country long before
its advantages as an element of economy were fully ap-
preciated here, or understood abroad, and there is au-
thority for the statement that as early as 1829 lap was
used on an engine designed to run a steam carriage in
New York, and in 1832 it was used on an engine of a
steamboat, because it was generally believed, even at
that time, that lap provided for the expansion of steam.
VALVES AND VALVE GEARS 53
It was soon recognized as an important improvement in
locomotive construction, but the economy of fuel it
brought about was not thoroughly understood. In fact,
many eminent mechanical engineers of that time were
of the opinion that the early opening of the exhaust
simply reduced the back pressure, -but that theory \^as
exploded when the Indicator was invented and applied
to the locomotive, for it was then demonstrated that
additional work was derived from the steam by using
it expansively.
The term lap, as previously explained, is used to des-
ignate the outside or steam edge of the plain slide-valve,
or the inner edge of the steam or admission port when
piston valves are used. Giving the valve lap consists of
extending or lengthening the metal of the valve face so
that the edges of the valve when in mid-position will
extend a distance over the steam ports, as shown by the
space between the letters A and B in Fig. 4. The exten-
sion is added so that the valve will close the steam port
before the piston completes its stroke, and the point
where the steam port is closed is called the point of cut-
off; this point depends on the speed of the engine, etc.
On some engines the inside edges of .the valve cavity
are slightly cut away so that they do not reach the inner
edges of the steam port, when the valve stands in mid-
position. This space is termed inside clearance. The
54
MODERN LOCOMOTIVE
great majority of locomotives have outside lap, but high-
speed engines have little or no inside lap, but are usually
given inside clearance.
The amount of lap to be given any engine depends, of
course, upon the character of the service it will be re-
quired to give, and it varies from J4 to i J/2 inches. Valves
having considerable lap are less likely to give faulty steam
Fig. 4.
distribution than valves having short lap. With a given
travel the period of expansion will be increased in pro-
portion to the extension of the lap.
Inside Lap.
Inside lap delays the release of steam and prolongs the
period of expansion; hastens compression and, as a re-
sult, increases it; tends to choke or retard the exhaust,
but does not effect admission or the point of cut-off.
Inside lap is indicated by the space between the letters D
and E in Fig. 4.
VALVES AND VALVE GEARS 55
No definite rule for determining the proper amount of
inside lap can be given, for there is a great difference
of opinion on the subject. The amount, however, is gen-
erally small, and depends upon the service the locomotive
is required to give, varying from zero to ^ of an inch.
In numerous locomotives, especially passenger locomo-
tives operated on a level track, the valves have no inside
lap, but for slow-speed engines, such as freight or switch-
ing locomotives, which are not required to ascend steep
grades, a small amount of inside lap will be beneficial.
The old practice of giving valves 1/16 of an inch in-
side lap has been almost altogetlier discontinued, and in
place of it the valves are made line and line, or given
inside clearance.
Inside Gleaxance.
Inside clearance, which is sometimes called exhaust
clearance, or negative inside lap, is given to a valve to
reduce the resistance to the movement of the piston, and
it should be sufficient to take full advantage of the nozzle
opening, for it delays compression, but hastens the ex-
haust release, and, as a result, produces a more speedy
engine. It opens the exhaust earlier, keeps it open longer,
and, as a result, reduces the back pressure, but it has no
eff'ect on the point of admission, or cut-off.
The detrimental effect of inside clearance is the sacri-
fice of water and fuel for increased speed. From an
56
MODERN LOCOMOTIVE
economical standpoint it is expensive, because it does not
obtain the advantages of steam expansion, but allows
the steam to be exhausted while at high pressure in the
cylinder. This can be overcome, however, by giving an
equal amount of inside clearance in the opposite eiids of
the cylinder in proportion to the exhaust edge of the
valve lip.
Fig. s.
Of late years the amount of inside lap has been gradu-
ally reduced, and at present valves are sometimes given
from Ys to 3/16 of an inch inside clearance on engines
operating at high speeds, but there is considerable differ-
ence of opinion regarding the beneficial results obtained
by the change.
Of course an increase of inside clearance will result
in a diminution of efficiency at slow-speed, but it is bene-
ficial on high-speed locomotives where long fast runs are
the rule, or on engines with small wheels which run at
a moderate rate of speed, for it causes the release of
steam in the cylinder to occur earlier and, as a result,
VALVES AND VALVE GEARS 57
compression later in the stroke. It all depends, how-
ever, upon the character of the service required of the
locomotive, and it may be safely stated that J4 of an
inch inside clearance is excessive for ordinary condi-
tions.
One of the early, if not principal, objections to giving
a valve inside clearance was the fact that it placed
the steam ports in communication with each other, as
well as with the exhaust port, and it was thought the
steam would blow through and be wasted. The extent
of time, however, during which the steam ports are in
communication depends partially on the amount of in-
side clearance, but principally upon the travel of the
valve and the speed of the engine.
By referring to the spaces indicated by the letters C
and C in the illustration. Fig. 5, it will be seen tliat the
intercourse between the two steam ports cannot result in
the anticipated loss of live steam, for both of the steam
port channels are acting as exhaust ports while they are
in .communication, so the only detrimental effect which
will develop is an interference between the exhaust steam
from the two ends of the cylinder which meets in the
exhaust cavity.
It may be added that the assumed detrimental effects of
inside clearance are entirely overcome, or rendered
58 MODERN LOCOMOTIVE
harmless, when the speed of the engine reaches, or ex-
ceeds, the rate of 50 miles per hour.
Admission.
The admission of steam behind the piston, to drive it
through its stroke, commences when the valve opens
the steam port for pre-admission, or lead. Admission
continues until the valve reaches the end of its travel
and then returns to the cut-off position, that is, to the
position at which the supply of steam to the cylinder
ceases. During this period of admission it is essential
that sufficient steam be taken into the cylinder to move
the piston for the work required during the entire
stroke.
Cut-Off.
The cut-off of the admission of live steam is one of
the most important events of the piston stroke. It does
not take place at the same point on the forward and back-
ward strokes, respectively, because the slanting, or ob-
liquity, of the connecting rod to the line of stroke results
in the piston being more advanced in the forward than
in the backward stroke than it should be to correspond
precisely with the position of the crank. This disparity
will be explained later on.
The percentage of the piston's stroke at which cut-off
occurs depends entirely upon the position of the reverse
VALVES AND VALVE GEARS
59
lever in the quadrant. For example, if the stroke of the
piston IS 32 inches, economy of steam can be obtained
by placing the reverse lever at a point which will cause
the valve to cut-off at about 8 inches, which would be
one-quarter of the piston stroke; and allowing the ex-
pansion of steam in the cylinder to supply the force for
the remaining 24 inches of the piston stroke. If, how-
FiG. 6.
ever, the desired speed cannot be obtained by such an
arrangement, the stroke may be increased by moving the
reverse lever farther away from the center of the quad-
rant. In fact, the point of cut-off is generally con-
trolled by local conditions, and it ranges from 6 to 20
inches.
The point of cut-off may be changed by altering the
lap of the valve, and this may also be accomplished by
changing the angular advance of the eccentric, and its
throw, without changing the lap of the valve.
6o MODERN LOCOMOTIVE
An early cut-off of the steam causes a restriction of
the steam port opening, especially near the point of cut-
off, where the current of the steam is rapid, and is fol-
lowed by an early release and exhaust closure, which
causes considerable increased compression.
An early cut-off is of material advantage, when an
engine is operated at high-speed, because it allows more
time for the exhaust steam to escape during the quick
movement of the valve.
The increased compression resulting from an early cut-
off may be considered an unavoidable evil and an in-
herent defect, or as a desirable feature and an incidental
advantage, of the combination slide-valve; but the point
of view depends entirely upon existing conditions and
varying theories;
An increase of the travel of the valve would generally
be considered the most effective remedy, or correction,
for compression, but where an unbalanced valve is used,
an extension of the valve will increase the unbalanced
area and the friction proportionally. When a contrac-
tion, or limitation, of the valve travel is considered neces-
sary, duplicate or supplementary ports may be used to
advantage. ' '
The contraction of the steam port opening is not of
much importance unless the steam is cut-off at an early
. VALVES AND VALVE GEARS 6 1
point in the stroke of the piston, and the most objection-
able feature is an early, or premature, release of steam.
The point at which cut-off occurs is shown by the small
arrow, when the valve is traveling to the left, as indicated
by the arrow A in Fig. 6.
Expansion.
Following the point of cut-off, the piston will be moved
by only the expansive force of the steam. That is, the
pressure of the steam confined in the cylinder behind the
piston will force" it forward, or backward, as the case
may be. This will increase the space in which the steam
is confined and there will be a fall in pressure approxi-
mately proportional to the increase in volume. Expan-
sion will continue from the time cut-off begins until the
valve opens for exhaust, that is, for only a small portion
of the. stroke ; a portion equal to the total of the inside
and the outside lap of the valve.
It must be apparent that if the opening of the valve
for exhaust could be delayed so that expansion would
continue until the pressure of the steam dropped to zero,
practically all of the available energy of the steam would
be utilized and converted into draw-bar pull. But such
an arrangement would be impracticable for an ordinary
cylinder, and in order to free the cylinders, the steam
62 MODERN LOCOMOTIVE
must be released earlier, to allow the steam time to
escape from the cylinder chamber before the piston be-
gins its stroke in the opposite direction.
CrompressioiL
The desire to eliminate compression, or to reduce it to
a minimum, is prompted by the fact that compression
shortens the effective power stroke of the engine. The
advantage of eliminating this resistance is generally ad-
mitted, for, although a portion of the energy exerted
in causing compression may be regained later on, it is
evident that only a part of it can reasonably be expected ;
but even if all of the power were returned there would be
a useless trading of energy for which no benefits would be
obtained.
Of course compression assists the lead opening, be-
cause it partly fills the clearance space with steam pres-
sure, helps to maintain the heat of the cylinder, prevents
loss from steam condensation, and also obviates the
shock which would otherwise be caused by the admission
of high-pressure steam for the return stroke. It must
be remembered, however, that no advantage is derived
from pressure on the crank pins when the piston is
within two inches of the end of its stroke, for it only
increases friction and performs no useful work. In fact
compression represents negative horse power developed
by the closing of the exhaust cavity.
VALVES AND VALVE GEARS 63
In high-speed engines compression is generally con-
sidered advantageous and essential, unless it produces
a pressure equal to or higher than the initial pressure,
but this occurs only a part of the time, usually when the
engine is running at the higher speeds with cut-off at
}4. or less. At other times compression does not fill the
clearance space and the shortage must be provided by
live steam from the boiler. But it should be remembered
that excessive compression, even in high-speed service,
will cause an engine to ride hard, and, if there be any
wear in the rods and boxes it will pound.
Compression commences at the point indicated by the
small arrow a when the valve is traveling to the left
as indicated by the large arrow A in Fig. 7.
Release, or Exhaust.
The point of release is just as important as the point
of expansion and compression, and may be considered
an aid of the two events, for each depends upon the
other. If release occurs too early the benefits of ex-
pansion are sacrificed and compression will be delayed ;
on the other hand if release occurs too late the beneficial
effect of expansion will be off-set by back pressure.
The valve should open for exhaust a little before the
piston reaches the end of its stroke, to give the exhaust
steam ample time to escape from the cylinder before the
64
MODERN LOCOMOTIVE
piston begins its return stroke. If the exhaust steam
was not discharged before the piston commenced its
return stroke, the cylinders would become choked and
each end would continually be working against the other
end.
This event of the valve stroke, release, is reached when
the exhaust edge of the valve reaches the exhaust edge of
Fig. 7. .
the steam port channel, which opens the port and permits
the steam, which has been confined behind the piston
to drive it through its working stroke, to escape to the at-
mosphere through the exhaust port.
The valve is in the same position for release as for
compression, but it is moving in the opposite direction
for the two events. The point of release is shown by
the small arrow b when the valve is traveling to the
right as indicated by the large arrow B in Fig. 7, and it
is in this position when the engine is said to exhaust,
or puff.
VALVES AND VALVE GEARS 65
/
Travel.
It must be clear, even to the novice, that the travel of
the valve is of necessity the most important event, or
feature, of the valve operation, for all other events of
the valve are controlled by the travel, and the slightest
change in the travel of the valve must, therefore, result
in a change in each of them.
The smallest amount of travel necessary to give a
full port opening must equal twice the amount of the
outside lap of the valve, plus twice the width of the
steam port.
On the other hand, the total width of the lap of the
steam port and the bridge combined, plus the over-travel,
if any, should not be more than one-half of the travel.
In order to secure full steam port opening during
any desired position of the stroke, the travel of the valve
must exceed the amount of outside lap and the width of
both steam ports.
The greater the travel the longer the steam port will
remain open for steam admission. It should be remem-
bered, however, that increased travel will require addi-
tional power to operate the valve, and will cause greater
wear on the valve and its seat, but these disadvantages
are partly overcome by the benefits resulting from bet-
ter steam distribution.
66
MODERN LOCOMOTIVE
Over-Travel.
The over-travel of a valve tends to choke the exhaust,
but insures sufficient port opening with an early cut-off,
and may be considered advantageous from the stand-
point of steam distribution, but the gain obtained, or
loss sustained, cannot be calculated by any fixed rule,
for the results depend upon circumstances.
DC
Fig. 8.
If over-travel causes the cut-off to occur too late, the
evil effects can be overcome by increasing the outside
lap, while delayed compression can be neutralized by
increasing the inside lap; if exhaust occurs too late, as
a result of over-travel, the inside lap may be sacrificed,
but if there is no inside lap the valve may be given
inside clearance.
The over-travel of a valve is shown by the space
indicated by the letter A in Fig. 8.
VALVES AND VALVE GEARS 6y
It will be observed that the valve is shown in two
positions on the valve seat. When in the position
marked C the valve has traveled to the left beyond the
point necessary to give the full steam port opening, and
is about to commence its return travel to the right, but
the inner edge of the valve has not traveled to the left
beyond the center of the exhaust port. On the other
hand, the position of the valve marked D shows that the
inner edge has not only passed the center of the exhaust
port, but the line marked E, which is drawn a distance
from the left hand bridge equal to the width of the steam
port. When a valve is given sufficient over-travel to
force it beyond the position corresponding to the line
E, or, in the position of the valve marked D, it is evident
that the exhaust port will be contracted, and this will
prevent the free escape of exhaust steam. Over-travel
hastens admission, delays cut-off, release, and compres-
sion, lengthens adrnission, and shortens the expansion
and compression periods.
Clearance.
It may be well for the reader to remember that there
is a difference between clearance, and the terms engine-
clearance y and piston-clearance, for they must not be
confounded, but we shall here treat clearance as all of
the space between the valve and the piston when the
piston is at the beginning of its stroke.
68 MODERN LOCOMOTIVE
The compression of steam by the advancing piston
will be increased or decreased, and its expansive force
is raised or lowered, in proportion to the amount of
clearance present between the valve and the piston.
A reduction of the clearance space is a distinct ad-
vantage, aside from its connection with proper cushion-
ing, for a reduction in this space adds to expansion, re-
duces the surface for steam condensation, and will prove
economical, for the clearance space must be filled with
live steam from the boiler to a considerable extent.
While direct and straight ports to the cylinder will, to
some extent, reduce the clearance, it is almost impossible
to design, or construct, a large locomotive cylinder with-
out allowing at least 8 or 9 per cent cylinder clearance.
Incidentally it may be said that piston-clearance is
given to prevent the piston from striking and burst-
ing either cylinder head, when the brasses on the con-
necting-rod wear and lost motion develops, or when
water accumulates in the cylinder. In locomotive cyl-
inders- piston clearance varies from j4 to ^-inch; it is
generally ^ of an inch.
Back-Pressure.
As all of the steam employed in driving the piston
cannot immediately escape through the port when the
valve opens for exhaust, a certain portion of it remains
in the cylinder for a time, and acts as an obstruction to
VALVES AND VALVE GEARS 69
the piston when it begins its return stroke; the amount
depending, to a considerable degree, upon the dimen-
sions of the port and of the exhaust nozzle, together with
the presence or absence of inside clearance of the valve.
There is always some back pressure in a locomotive
cylinder, and a certain amount of it is necessary to
create the draft, but an excessive amount will cause a
serious loss of efficiency, and its presence can be readily
detected by the increased amount of fuel consumed.
The retarding force of back pressure against the
piston in locomotives with simple cylinders is about 7
to 9 pounds per square inch, but it may increase slightly
as the speed increases, for the amount of condensation
is not exactly constant at all speeds. It should not,
however, be greater than lo pounds at a speed of 20
miles per hour, or 15 pounds at 50 miles per hour.
Lead.
It is generally stated that lead is given to a valve in
order that steam may be admitted between the piston and
the cylinder head, just before the completion of the
piston's stroke, to assist compression in cushioning, or
gradually retarding, the piston, by tempering the sudden
reversion and bringing the cranks smoothly over their
centers, but such broad statements are incorrect and mis-
leading.
yo MODERN LOCOMOTIVE
As a matter of fact the advancing piston is brought to
a state of rest by the steam compressed between the
piston and the cylinder head, with the aid of preadmis-
sion ; and the combined pressure of compression and pre-
admission in the piston clearance is sometimes equal to,
if not greater than, initial pressure; as a result the
steam admitted by lead can exert no force against the
piston until the piston begins its return stroke, when the
compressed steam expands.
Thus it is really preadmission, and not lead, which
admits steam before the completion of the stroke. How-
ever, lead accomplishes this indirectly, for, without lead,
there could be no preadmission.
Lead is given to increase the pressure in the clearance
space of the steam port channel and to insure greater
steam port opening for an abundance of full steam pres-
sure, to assist expansion of the compressed steam be-
hind the piston at the very beginning of the piston's
stroke, when full steam pressure in the cylinder is most
advantageous ; it also helps to maintain a satisfactory sup-
ply of steam throughout the period of admission. Lead
is not a part of the valve proper, but the point at which
it begins is indicated by the letter A in Fig. 9.
No definite rule governing the proper amount of lead
to be given in all cases can be stated, for the amount nec-
essarily varies slightly with changes in speed, or the
VALVES AND VALVE GEARS
71
amount of compression, and can only be accurately de-
termined by the use of the Indicator ; in fact, the amount
of lead which would be proper and beneficial in one class
of service might be detrimental in another kind of work.
For a long time it was the practice to allow from
3/16 inch negative to % inch positive lead, but of late
years there has been a tendency to reduce the full gea**
lead, and the amount now employed varies from 3/12 to
1/16 of an inch.
Fig. 9.
Good results can only be obtained by allowing just
sufficient lead to fill the clearance space completely; an
additional amount of lead would be wasteful of steam
and prove unsatisfactory. For example, in starting an
engine, or working it at slow speed, lead is undesirable,
and should be sacrificed as much as possible, for it tends
to retard the movement of the piston at the end of its
stroke, and deprives the engine of a quick start. On
the other hand, as the speed is increased, the reduced
amount of time allowed for the admission of steam to the
i
72 MODERN LOCOMOTIVE
cylinder renders a certain amount of lead necessary, and
an increase of lead at high-speed is desirable and bene-
ficial, because it imparts a larger port opening in the short
cut-offs.
The beneficial results obtained by giving the valve
lead have long been recognized, and we doubt whether
any locomotive at the present time is operated without
some lead.
It may also be noted that a proper reduction of the
amount of lead will give a more efficient steam distribu-
tion, because such a reduction of lead will not neces-
sarily reduce the maximum port opening at short cut-off
sufficiently to materially impair the admission of steam
by wiredrawing, for the speed of the piston at the quar-
ter stroke is comparatively slow.
Lead is given to the valve by shifting the eccentric on
the shaft to or from the crank-pins, the directing depend-
ing, of course, upon whether a direct or an indirect valve
gear is used.
Lead increases when the reverse lever is moved toward
the center, on an engine equipped with the Stephenson
valve gear, because, as the lever is hooked up toward
the center, both eccentrics influence the position of the
valve. The lead of an engine equipped with the Stephen-
son valve gear can also be changed by moving the eccen-
trics toward or away from the crank-pins, depending
VALVES AND VALVE GEARS 73
upon whether the lead is to be increased or decreased,
or by reducing the lap of the valve if the eccentrics are
to be retained in their normal position.
On the other hand the lead of an engine equipped
with the Walschaert, or other radial type of valve gear,
is constant, and can only be changed by changing the
proportions of the combination, or lap and lead lever,
or by reducing the lap of the valve. However, special
"lead controllers," which will be described later on, are
often employed to permit the control of lead with outside
radial gears.
Even when the greatest care is exercised in designing
and erecting a locomotive, a certain amount of lost mo-
tion in the driving boxes, and other working parts, soon
develops, and the effect of such lost motion will result
in delaying the movement of the valve if lead is not given,
and, in some instances, will result in allowing the piston
to begin its return stroke before steam is admitted to the
cylinder. Of course this causes a certain amount of
pounding, at each end of the piston stroke, if a proper
amount of lead is not given.
Preadmission.
Preadmission is always subject to change, even when
the lead is constant, and is, under ordinary conditions,
the greatest factor in compression, for it commences when
74 MODFRN LOCOMOTIVE
the valve port opens for lead and ends when the crank
pin is on center, or at the point where lead begins.
The accompanying outline drawing, Fig. lo, clearly
shows the commencement and brief duration of pread-
mission.
By referring to the illustration it may be seen that
preadmission commences in the right-hand port when
the valve begins to uncover the port, when the crank-pin
center, which is connected to the piston, is in the posi-
tion shown; and it ends when the crank-pin is on dead
center, that is, when the piston reaches the end of its
stroke to the right.
This small movement of the piston is just sufficient to
force the valve to the left to give full lead opening in
the right-hand port.
Of course preadmission is the result of lead, but, during
the time the main pin is traveling from the preadmission
to the lead position, the movement of the valve is so
rapid, while that of the piston is so slow, that pread-
mission may be considered neghgible; at least, so far as
starting is concerned. In fact, with certain valve gears,
lead in full gear does not give more than 1/32 of an inch
preadmission. But, on the other hand, when the re-
verse lever is moved toward the center of the quadrant,
(hooked-up), from % to i>4 of an inch preadmission
VALVES AND VALVE GEARS
75
may be secured, but it may be as short as ^ of an inch
with other valve gears.
There is, however, considerable difference of opinion
regarding the beneficial results to be obtained by pre-
admission, and many able men who have given the matter
serious consideration are inclined to believe that pread-
mission is of no special benefit, for the reason that com-
pression is fairly well developed before preadmission
commences.
Fig. io.
Wiredrawing.
As the amount of space available for the steam ports
of a locomotive is limited, their area is necessarily small,
even when they are fully opened, and their outline is
far from being straight; as a result the passageways for
the admission of steam from the boiler to the cylinder
are restricted so that wiredrawing is unavoidable, to a
certain extent. In such cases the steam is said to be
throttled on its way from the boiler to the cylinder, and,
in consequence, its pressure behind the piston is reduced
>]() MODERN LOCOMOTIVE
as the piston proceeds on its stroke, until, at the point of
admission, it falls below the boiler pressure.
It is generally believed that wiredrawing in locomotive
service is, to any extent, objectionable, and a thing to
be avoided, but, as a matter of fact, it is always present,
and renders useful service in certain classes of work.
It aids in the maintenance of uniform boiler pressure for
various rates of speed and is, therefore, beneficial from
an economic standpoint.
For example, take an engine traveling up a grade at
the rate of 20 miles per hour, with the throttle and re-
verse-lever in a position to require a moderate working
load on the boiler; when the apex, or top, of the grade
is passed, the load will be reduced in proportion to the
grade, and the speed will increase twice or three times
that maintained in ascending the grade, but the throttle
and reverse-lever may be allowed to remain in their
former positions, for the wiredrawing action will answer
the demand, and prevent the cylinder from demanding
more steam than the boiler can supply, without reducing
the speed or maximum capacity of work.
In fact, wiredrawing results in economy of steam in
proportion to the increase of speed from about 20 to 50
miles per hour, but for greater speeds the evil effect is
increased, for it produces increased steam consumption.
VALVES AND VALVE GEARS ^^
Relative Positions of the Piston and Crank Pin.
As the connection between the crosshead and the
piston is rigid, their positions corresp'ond exactly ; hence,
if we know the motion of one of them> we also know
the motion of the other. We will therefore dispense
with a view of the piston in our illustrations for the
present, and ignore the crosshead connection ; proceeding
on the theory that the piston is connected to the crank by
a link. This link is generally termed a connecting rod,
and is employed in changing the reciprocating rectilinear
motion of the piston into the circular motion of the
crank pin.
»
If the eccentric rod were of indefinite length, or if
its obliquity were neglected, then, with the. crank pin
at any position between the front and back dead centers,
the corresponding position of the piston could be ascer-
tained by drawing a perpendicular line upon the diam-
eter of the crank pin circle, which may be said to repre-
sent the stroke of the piston. For exampje, when the
crank had traveled one-quarter of a revolution, the piston
would be in the center of its stroke, etc. In practice,
however, the changing angles of the connecting rod dur-
ing the different periods of the • crank pin revolution
must be taken into consideration.
Any irregularities imparted by the crank pin to the
motion of the piston will be conveyed into the motion of
78
MODERN LOCOMOTIVE
the valve, but the throw of the eccentric rod is generally
so small in comparison with that of the crank pin that
it is inappreciable and may be disregarded, for the eccen-
tric rod is proportionally longer than the connecting rod,
and it follows that the distortions in the motion of the
valve are necessarily much less than those in the motion
of the piston.
Fig. II.
The obliquity, or angularity, of the connecting rod
can be more forcibly impressed upon the reader's mind
by the use of an illustration than by any written descrip-
tion we might give, so we shall proceed to construct
Fig. II, to show the travel of the piston, crank pin and
connecting rod. The length of the connecting rod, which
is measured from the center of the crank pin to the
center of the crosshead pin, varies in practice from four
to eight times the length of the crank, so, for the pur-
pose of this ilkistration, we will use a connecting rod
six times the length of the crank.
First we will draw the circle, a p b d, which is the
crank pin circle, with the diameter equal to the travel
»
VALVES AND VALVE GEARS 79
of the piston. Let C represent the center of the crank
shaft, and the horizontal Hne, A h, which passes through
the center of the circle C, the center line of motion of
the crosshead, piston rod and piston. Now from the
point a, of the circle as a center, and with a radius
equal to the length of the connecting rod, strike an arc
cutting the line A b in the point A. This point will be
the center of the crosshead pin at the forward end of
its travel. From the point ^ as a center, and with the
same radius, strike another arc cutting the line A b
at the point B, and this point will be the center of the
crosshead pin at the back end of its travel. Since the
distance between the points A and B represent the full
length of the piston stroke, we may find the center of
the stroke by striking an arc on the line A b from the
center C of the circle, which will equally divide the dis-
tance between A and B ; and we will mark the point O
on the line A b. Now from the point O, and with a
radius equal to the length of the connecting rod, we will
draw the arc o C m, and mark the points o and m where
it intersects the crank pin circle ; the two points o and m
will be the centers of the crank pin when the piston is
at the center of its stroke.
By referring to the illustration again it will be noticed
that the end of our connecting rod has reached its
quarter stroke and is at the point p, so, with a radius
8o MODERN LOCOMOTIVE
equal to the length of the connecting rod, we will strike
?.n arc cutting the line A h in the point D. The point p
bisects the semi-circumference which extends from a to
b, but it may be readily observed that the point D does
not bisect the stroke A B ; in fact the point D is much
nearer the B end of the stroke than it is to A.
From this we see that during the first half stroke of
the piston the crank pin travels from a to o, and during
the second half stroke of the piston the crank pin travels
from o to b. Since the motion of the crank must be
uniform, the average speed of the piston during the first
half stroke will be a little greater than during the second
half stroke ; and this difference in the speed of the piston
is due to the obliquity of the connecting rod.
Now, assuming that our illustration of the variation
in the piston's travel, between the first and the second
half of its stroke, is clear, the reader may find it profit-
able to ascertain the movements in the different periods
of the stroke.
To assist in the continuation of our examination, let
us make a new illustration, making the crank pin circle
and piston travel the same as in Fig. ii, but on a slightly
larger scale. We shall, however, employ, in Fig. 12, a
connecting rod three times the length of the crank, in-
stead of six times its length, as used in Fig. 11. A
connecting rod of this length could not be used in loco-
VALVES AND VALVE GEARS
8l
motive service, and it is only adopted here to empha-
size the movement of the piston at different positions.
Our next step will be to divide the piston travel and
the upper semi-circumference of the crank pin circle
into eight equal parts, which we will number to corre-
spond. Advancing the short connecting rod from the
point a, which represents the front dead center, to the
Fig. 12.
point I on the semi-circumference of the crank pin cir-
cle, we strike an arc cutting the line A b in the point c,
which will indicate the position of the crosshead pin,
and, in a similar manner, from each of the other figures
on the semi-circumference of the crank pin circle we
strike similar arcs and mark with letters to correspond.
The crank pin moves at a symmetrical rate of speed
through the divisions we have marked on the semi-cir-
cumference of the crank pin circle, yet we find from
an examination of Fig. 12, that the movements of the
crosshead pin, and therefore of the piston, from c to d.
82 MODERN LOCOMOTIVE
and from e to f, on the line A b, are not equal. In fact,
it shows that the piston will, at the commencement of
its stroke, move comparatively slow, and increase its
speed as it approaches the center of the stroke, and
when the piston is moving away from the center of the
stroke, its speed is constantly decreasing.
This variable motion of the piston is caused chiefly
by changing the rectilinear, or straight, motion into a
uniform circular motion, and to some extent, by the angle
formed by the center line of the connecting line and
the horizontal line A b, an angle which is constantly
changing during the stroke.
Various expedients have been adopted to overcome,
or neutralize, the evil effects due to the angularity of
the connecting rod, but it has been found that fairly
good results can be obtained, at small expense, by setting
the link saddle pin back.
Relation Between the Valve and Eccentric, or
Crank Arm.
Thus far we have confined our discussion to the valve
proper, and the valve events, referring to the connection
of the valve with the cylinder and piston to a limited
extent, and with but casual reference to the parts by
which the movement of the valve is controlled.
We now feel that the reader should begin the study
of the eccentric, or crank, and the relative position of
VALVES AND VALVE GEARS 83
it to the corresponding movements of the valve. Fol-
lowing our original plan we shall first look at the most
early and most common methods of transmitting the
reciprocating motion of the piston to the valve through
the rotating motion of the eccentric.
The Eccentric.
Literally, the word eccentric means, "out from the
center." While there is not much similarity in the
appearance of an eccentric and a crank arm, they are
used for the same purpose, and give exactly the same
results. It may also be said that there is, in reality, noth-
ing mysterious about an eccentric, for it is essentially a
crank, whose length is equal to the radius of the throw
of the eccentric with the pin increased to include the
shaft.
A crank arm can only be used at the end of a shaft,
while an eccentric may be attached at any point desired
along the shaft, without reducing (by cutting or divid-
ing) the strength of the shaft, and it is the latter
feature which often decides in a selection between the
two.
To make the subject more clear we present two views
of the eccentric, and one of a common crank, on page 84.
It will be observed that Fig. 14 shows the eccentric in
full, while Fig. 13 shows it in section, and Fig. 15 shows
a common crank.
MODERN L0CX)M0T1VB
Fig. 13.
Fig. 15.
VALVES AND VALVE GEARS 85
In Fig; 14, the eccentric proper, A A, which rotates
with the shaft and corresponds to the crank arm, is called
the eccentric sheave. The eccentric sheave is surrounded
by a metal strap, or band, commonly called the eccen-
tric strap, B B, inside of which the eccentric sheave
is free to turn. Both the sheave and the strap are
made in two halves, so that they can be readily put on
or taken off; the two pieces of the sheave are parted
on a Hne passing through the center of the shaft at
right angles to the horizontal center line of the eccen-
tric, and are bolted together and rigidly keyed or fast-
ened by studs to the shaft. The strap is grooved so
as to prevent it from becoming displaced or getting off
the sheave, and it is bolted together at its top and bot-
tom.
An oil cup, e, Fig. 14, is usually cast solid on one
half of the str^p, for particular care must be given
to the lubrication, the friction of eccentrics being much
greater than that of cranks because they have larger
sliding surfaces, between the sheave and the strap. It
may also be noted that an eccentric requires more metal
for its construction and space for its operation than
a crank; it also absorbs more power than the crank, as
a result of the greater leverage at which the friction
acts, and it is used in preference only where the throw
is comparatively short.
86 MODERN LOCOMOTIVE
A crank is used for converting the rectilinear
motion of the piston into .rotary or circular motion, while
an eccentric is usually employed for converting the rotary
or circular motion of the shaft back into the straight
motion of the valve.
When the valve receives its motion from an eccen-
tric, the periods of steam distribution are necessarily
controlled by the position of the eccentric, and they oc-
cur earlier or later in the stroke as the eccentric is
turned forward or backward on the shaft.
Now, referring to Fig. 14, we find that the point
C is the center of the shaft, and the point D is the cen-
ter of the eccentric sheave. As the sheave revolves
with the shaft the point D will describe the small dotted
circle on the shaft, whose center is the center of the
shaft. As a result when half of a revolution is com-
pleted, the eccentric strap, B B, will be moved horizon-
tally a distance equal to the diameter of the dotted
circle, which equals the throzv of the eccentric, or the
travel of the valve. The distance between the center
of the shaft C and the center of the sheave D equals
the length of the crank arm, and is termed the radius
or eccentricity of the eccentric, which is one-half of
the throw. All movements of the eccentric are trans-
mitted to the valve bv means of an eccentric rod and
valve stem, which connect the two.
VALVES AND VALVE GEARS 8/
In practice, the travel of a locomotive valve does
not always equal the throw of the eccentric; the differ-
ence may be attributed- to the influence of the link, and,
in many cases, to the unequal length of the rocker arms.
With this brief description of the eccentric, and ex-
planation of its use, we shall proceed to develop its
relation to, and connection with, the movement of the
valve.
Position of the Eccentric for a Valve Without
Lap.
In practice the eccentric is always mounted on the
crank-shaft, and, if the valve has no lap and no lead,
the center line of the eccentric must be perpendicular
to the center line of motion of the valve gear when
the piston is at end of its stroke and the valve stands
in its central position.
The eccentric must, in all cases, travel ahead of the
crank, and when the connection between the valve and
the eccentric is direct, as in Fig. i6, and the piston is
at the end of its stroke, the crank is on dead center;
therefore, the valve must be in its central position, and
the center of the eccentric must be midway between the
two dead centers.
In such a case, when the piston begins to move toward
the right-hand end of the cylinder, the center of the
88
MODERN LOCOMOTIVE
eccentric will turn, with the crank, to the right, and pull
the valve in the same direction, so that the left-hand
edge of the valve face will open the left-hand steam
port. This admits steam to the left-hand steam port,
behind the piston, and drives it in the desired direc-
tion, while the right-hand edge of the valve will un-
cover the right-hand steam port, and permit the steam
in front of the advancing piston to escape.
Fig. 1 6.
If the center of the eccentric was placed one-
quarter behind the crank, midway between the two dead
centers, it is apparent that when the piston commenced
•
its stroke to the right the valve would be moved to the
left, thereby uncovering the right-hand steam port for
the admission of steam in front of the piston. If, how*
ever, we turn the crank in the opposite direction, that is,
to the left, the valve will uncover the left-hand steam
port and admit steam behind the piston and the engine
will move in the opposite direction. In other words, if
the center of the eccentric is placed 90 degrees ahead
VALVES AND VALVE GEARS 89
of the center line of motion of the valve gear the shaft
will rotate to the right; if placed 90 degrees behind the
center line of motion of the valve gear the shaft will turn
to the left.
We shall assume that the parts, shown in Fig. 16, are
about to move in the direction of the arrows. When
the crank reaches the top quarter, the eccentric center will
be on the back dead center, the valve will have reached
the end of its travel to the right, and the piston will have
almost reached the center of its stroke. The piston
would be exactly at the center of its stroke but for the
angularity of the connecting-rod, which has been ex-
plained. When the parts have moved another quarter the
crank will be on the back dead center, the eccentric
will be on the lower quarter, the piston will have reached
the end of its stroke to the right, and the valve will
have moved to the left, so that it stands central. An-
other quarter movement will place the crank on the
lower quarter, the eccentric center on the forward
dead center, the valve at the end of its travel to the
left, and the piston almost in the center of its stroke.
The final quarter movement will place the parts in the
positions they originally occupied in the illustration. (It
must be obvious that a valve of this pattern will not
admit steam into the cylinder to start the movement of
90 MODERN LOCOMOTIVE
the engine from a state of rest, for the valve opens just
after the stroke of the piston commences.)
The primitive form of valve illustrated, which just
covers the steam ports when in mid-position, can not be
used with economy, as it allows steam to follow the piston
for the whole of the stroke, and does not permit the use
of its expansive properties, for the simple reason that,
at the instant the admission of steam ceases, the exhaust
of the same body of steam must immediately commence,
thereby sacrificing the beneficial results obtained from
compression.
As it has been shown that this elementary valve is
extremely wasteful, and therefore impractical, let us
modify it by extending its face so that when the valve
is in mid-position it will overlap the steam ports. Thus
we may see what effect the addition of lap to the valve
will have upon the position of the eccentric.
Position of the Eccentric for a Valve With Lap.
Now that we are about to examine the positions of the
eccentric for a valve with lap, it may be well to again
refer to our definitions of the terms "linear advance'* of
the valve, and ''angle of advance" of the eccentric. It
will be found that the positions of the two are closely
related, and, in a sense, dependent upon each other, yet
VALVES AND VALVE GEARS
91
the distinction between the terms is of great importance
and should be thoroughly understood.
When the valve is given lap, that is, when the face of
the valve is lengthened, it will be necessary for the linear
k
yALVE TRAVEL
•^^Ai
Fig. 17.
travel of the valve to be increased a distance equal to
the outside lap, for the admission of steam to take place.
The valve must travel the length of the lap plus the width
of the port, if the port is to be fully opened, and, of
92 MODERN LOCOMOTIVE
course, increased linear travel means increased throw, or
advance of the eccentric, which will require a change in
the position of the eccentric on the crank shaft.
In Fig. 17 we have shown the valve in two positions,
and placed the eccentric circle above the same, so that
the reader may readily observe the effect that a move-
ment of either the valve or the eccentric will have upon
the other. The dotted lines represent the valve standing
in the center of its travel, and, for reference, we have
marked it A. The other view shows the valve at the
commencement of the piston stroke, and is marked B,
If we assume that the piston is at the beginning of its
stroke to the right, it is obvious that the valve A is not in
a position to admit steam to the left-hand port; in fact
to admit steam into the cylinder behind the piston the
valve A must be moved to the right from its central
position until it has opened the left-hand port, and, if
the valve is given lead, an additional amount equal to
the lead. As a result the center of the eccentric, at the
beginning of the piston's stroke, cannot remain in the
position shown in Fig. 16, that is, at right angles to the
crank, but must be advanced (in this case, to the right)
an additional amount, equal to the lap and the lead com-
bined, as shown in the illustration. When the necessary
amount of linear advance is given to the valve A, it will
occupy the position of the valve B and admit steam
VALVES AND VALVE GEARS 93
behind the piston at the beginning of its stroke to the
right.
As a result of the change in the position of the
eccentric all of the events, effected by the valve will be
completed earlier; that is, the port for the admission of
steam will be parlffy opened at the beginning of the
piston's stroke, and it will be closed before the end of the
stroke, so that the steam will be allowed to expand during
the period from cut-off to release. The exhaust will
also be closed before the end of the stroke, and the un-
discharged steam trapped in the cylinder will undergo
compression.
Relative Positions of the Valve and Piston.
Now that the reader is familiar with the various posi-
tions of the valve on its seat for the events of the stroke,
and the position of the eccentric and crank for a valve
without lead or lap, let us compare the different positions
of a valve with lap to the corresponding positions of
the piston.
The motion of the piston is not symmetrical, as has
already been explained, but we shall here disregard this
slight difference due to the angularity of the connecting-
rod.
Admission, or lead opening. In Fig. i8 the slide valve
is shown at the point of lead opening, that is, the left-
hand port is open to the admission of steam into the head-
94
MODERN LOCOMOTIVE
end of the cylinder. These positions are shown on a
larger scale in Figs. 6 for admission, and 9 for lead.
The eccentric arm, instead of being at right angles to
the crank at the beginning of the stroke, as shown in
Fig. 16, is set ahead an amount equal to the angular
advance. The reason for this is, as fh*eviously explained,
that the valve, instead of standing central as it would if
it had no lap or lead, must be advanced, or set ahead
\
/
Fig. 18.
an amount equal to the outside lap plus the lead, in order
that steam may be admitted into the cylinder at, or a
little before, the commencement of the stroke of the
piston. The crank pin is on the forward dead center,
and the piston is about to begin its stroke, so the admis-
sion of steam behind the piston will now begin, and con-
tinue, through the left-hand port, behind the piston, until
the valve returns to close the left-hand port.
Cut'Off. When the valve has traveled to the end of
its stroke to the right, in order to fully open the left-
VALVES AND VALVE GEARS
95
hand port to admission, it must return in the direction of
the arrow to the position shown in Fig. 19. The
eccentric arm will have moved from its position in Fig.
18 to that in Fig 19, in the direction indicated by the
arrow. During this period a corresponding movement
of the crank takes place, causing the piston to assume
the position shown m Fig. 19. It will be noticed that
the piston has alread\ completed more than half of its
Fig. 19.
stroke to the right. A further movement of the valve
in the direction of the arrow will close the left-hand
port to the admission of steam, that is, cut-ofF takes place.
This point is more clearly illustrated in Fig. 6. Expan-
sion will now commence in the head-end of the cylinder,
and the force of the expanding steam will cause the
piston to continue its movement to the right.
Compression. As the position of the piston in Fig. 20
is reached, the valve will have moved to cover the
right-hand port, as shown in the illustration, and also in
Fig. 7. The unexhausted steam trapped in the crank
96
MODERN LOCOMOTIVE
end of the cylinder will be compressed by the expansive
force of the steam previously admitted to the head-end
of the cylinder acting upon the piston and moving it
to the right. Expansion, theoretically, should cease im-
mediately at the point of release, but in practice there
is a gradual, although rapid, decrease in pressure on the
piston, causing a slight prolongation of expansion.
^//y//yy^^///^///y'/yy>m'//^
Fig. 20.
Release. Because the valve shown in these illustrations
is line-and-line with the steam ports, that is, it has no
inside lap or clearance, the point of the commencement
of compression in the crank-end corresponds to the point
of release in the head-end. If the valve had inside lap,
release would follow compression; if it had clearance,
release would take place before compression began. This
is readily understood by referring to Fig. 20. Release
is also shown in Fig. 7 on an enlarged scale. Exhaust
will continue from the point of release shown in Fig. 20
at the left-hand port, until the point of compression
on the return stroke of the piston.
VALVES AND VALVE GEARS
97
Admission, — Crank-end. Compression will continue
from the point shown in Fig. 20 to that shown in Fig. 21,
where the valve is just about to uncover the right-hand
port to admission. It may be seen from the position of
the crank that the piston has not yet reached the end
of its stroke. The reason for this is that pre-admission
commences a little before the point of full lead opening,
and therefore before the completion of the stroke, is
Fig. 21.
reached. The eccentric arm, too, must travel an amount
equal to the lead opening of the valve in order to reach a
point exactly opposite that shown in Fig. 18.
Valve With Rocker Arrangement.
The reader should bear in mind that the foregoing
illustrations are primarily intended to show the cor-
responding positions of the piston and a valve with lap,
and the various positions of the eccentric and crank are
shown only for that purpose.
It may be observed in the illustrations that the valve
is not in line with the eccentric, and for this reason, if
98
MODERN LOCOMOTIVE
for no other, the direct connection between the valve and
eccentric would be impracticable. As a result of this angle
between the eccentric rod and the center line of motion,
the speed of the valve would vary during the stroke, even
though the eccentric rotated at a constant speed. For
this reason a rocker, of the type shown in Figs. 22 or 23,
is interposed between the eccentric and the valve, and is
used merely to connect the eccentric rod and the valve
MM »■
Fig. 22.
rod. While it affects the position of the eccentrics, and
often the travel of the valve, the rocker will not neces-
sarily affect the rules regarding the valve construction.
In Fig 22 the rocker is pivoted at A, and the rotating
motion of the eccentric imparts a backward and forward
motion to the rocker through the connection C. This
reciprocating movement is applied to the valve through
the valve stem connected to the rocker at B.
It is often more convenient to place the pivot of the
rocker between the valve stem connection and the con-
nection with the eccentric rod, as shown in Fig 23 at
VALVES AND VALVE CEARS
99
the pcMnt A. Now, in order to impart to the valve the
same motion as that in Fig 22, the eccentric must be
set ahead 180 d^jees, for it will be seen, as indicated
by the arrows, that in this illustraticm the valve stem
and eccentric rod move in opposite directicwis. Thus,
even though the eccentric rod moves in the direction op-
posite to that in Fig. 22, the valve rod moves in the same
direction as formerly, because the pivot A of the
Fig. 23.
rocker is placed between the two connections. Either
type of rocker may therefore be used with the same re-
sults.
The rocker mav also be used so as to make the throw
of the eccentric less than the travel of the valve, for,
as the distance between the points B and C, Fig. 22, is
increased, the throw of the eccentric for a given travel
of the valve is decreased.
Direct and Indirect Valve Motion.
The rocker arm is usually the means by which the
motion imparted to the eccentric is reversed. With the
lOO MODERN LOCOMOTIVE
Stephenson link motion, if both arms extend in the same
direction from the rocker shaft, the motion is direct.
However, if they extend in opposite directions from the
shaft, one up and one down, the motion is reversed, and
the valve is indirect.
With the more modern radial valve gears, the motion
is direct when the link block is working below the cen-
ter of the link, when it has the same direction of motion
from the eccentric to the valve. But when the link
block is working above the center of the link, the motion
is indirect. Therefore, reversing the engine, or placing
the link block above the center of the link, changes the
valve motion from direct to indirect.
Inside admission valves, as the modem piston valve,
also influence the valve motion. When the valve admits
steam from the inside, it must move in the .opposite di-
rection to the outside admission valve, that is, in a direc-
tion opposite to that of the piston at the commmencement
of the piston stroke. To accomplish this, the valve may
be driven direct, without a rocker, leaving everything
else the same. The rocker will give the desired motion,
however, if both eccentrics are moved half way round
the axle.
The following is a simple means of distinguishing be-
tween direct and indirect motion :
VALVES AND VALVE GEARS lOl
If the crank pin and eccentric are on the same side of
the driving shaft, and a rocker is provided to reverse
the motion, the valve is indirect, outside admission. But
if the crank pin and eccentric are together without a
rocker arm, the valve has inside admission, direct.
If the crank pin and eccentric are on opposite sides
of the drifting shaft, with a rocker to reverse the motion,
the valve has inside admission, and is indirect. With
crank pin and eccentric opposite without a rocker, how-
ever, the valve has direct motion, and is outside admis-
sion.
The distinction may be stated briefly as follows : When
the eccentric rod moves forward, and produces a fore-
ward movement of the valve, the motion is direct. But,
if when the eccentric moves forward, the valve moves
back, the 'motion is indirect.
Problems Relating to Lap of the Slide Valve.*
To find the point of cut-off when the lap and travel of
the valve are given, the valve to have no lead.
Example, — Lap of valve is one inch ; travel, 5 inches ;
no lead ; stroke of piston, 24 inches. At what part of the
stroke will the steam be cut off
We must first find the center c. Fig. 24, of the circle
abm, whose circumference represents the path of the
•This article by the late J. G. A. Meyer, M. E., In The Locomo-
tive Up-to-Date, Is reproduced by permission of the publishers.
102 MODERN LOCOMOTIVE
center of eccentric, and this is found by placing the valve
in a central position, as shown in dotted lines in this
figure. Then the edge c of the valve will be ttie center
of the circle. The valve drawn in full lines shows its
position at the commencement of the stroke of piston;
and since the valve is to have no lead, the edge G will
'^
■•
^^^
.. .
t>cr
tjM'-i 1
■I wma
m~^ t *j t ,
"^
:>
I
Fig. 24.
coincide with the outer edge of the steam port. Through
the edge O draw the line i h perpendicular to the line
A B; the line i h will intersect the circumference a b m
in the point v, and this point will be the center of eccen-
tric when the piston is at the beginning of its stroke.
Now, assume that the circumference a b m also repre-
sents, on a small scale, the path of the center of the
crank-pin ; then the diameter y x oi this circle will repre-
VALVES AND VALVE GEARS IO3
sent the length of the stroke of the piston; the position
of this diameter is found by drawing a straight line
through the point y (the center of the eccentric when the
piston is at one end of its stroke) and the center c. Also
assume that the point y represents the center of the
crank-pin when the piston is at the beginning of its
stroke. To make the construction as plain as possible,
divide the diameter yx into 24 equal parts, each repre-
senting one inch of the stroke of piston, and for con-
venience number the divisions as shown. The arrow
marked i shows the direction in which the valve must
travel, and arrow 2 indicates the direction in which the
center y must travel. Now it must be evident, because
the points y and O will always be in the same line, that
during the time the center y of the eccentric travels
through the arc y g, the valve not only opens the steam
port, but, as the circumference ah m indicates, travels
a little beyond the port, and then closes the same, or, in
short, during the time the center of eccentric travels from
y to g, the port has been fully opened and closed; and
the moment that the center of eccentric reaches the point
g, the admission of steam into the cyHnder is stopped.
We have assumed that the point y also represents the
position of the center of crank-pin at the beginning of
the stroke; and, since the crank and eccentric are fast-
ened to the same shaft, it follows that during the time
104 MODERN LOCOMOTIVE
the center of eccentric travels from > to g' the crank-
pin will move through the same arc, and when the steam
is cut off the crank-pin will he at the point g. There-
fore, through the point g draw a straight line g k per-
pendicular to the line y x; the line g k will intersect the
line y x in the point k, and this point coincides with the
point marked 20 ; hence the steam will be cut off when
-zrXl j
Fig. 25.
the piston has traveled 20 inches from the beginnii^ of
its stroke.
Lead Will Affect the Point of Cnt-Off.
In Fig. 24 the valve had no lead; if, now, in that figure,
we change the angular advance my c oi the eccentric
so that the valve will have lead, as shown in Fig. 25, then
the point of cut-off will also be changed. How to find
the point of cut-off when the valve has lead, is shown in
Fig. 25.
VALVES AND VALVE GEARS IO5
Example.— The lap of valve is i inch, its travel 5
inches ; lead J4 of an inch (this large amount of lead has
been chosen for the sake of clearness in the figure) ;
stroke of piston, 24 inches; at what part of the stroke
will the steam be cut off?
On the line A B, Fig. 25, lay off the exhaust and steam
ports ; also on this line find the center r of the circle ab m,
in a manner similar to that followed in the last con-
struction, namely, by placing the valve in a central posi-
tion, as shown by the dotted lines, and marked D, and
then adopting the edge c of the valve as the center of the
circle ah m; or, to use fewer words, we may say from the
outside of the edge .y of the steam port, lay off on the line
A B a. point c whose distance from the edge ^ will be
equal to the lap, that is, i inch. From c as a center, and
with a radius of 2j4 inches (equal to one-half of the
travel), describe the circle a b m, whose circumference
will represent the path of the center of eccentric. The
lead of a valve in a locomotive is generally 1/32 and
sometimes as much as 1/16 of an inch, when the valve is
in full gear, but for the sake of distinctness we have
adopted in this construction a lead of ^ of an inch in
full gear. Draw the section of the valve, as shown in
full lines, in a position that it will occupy when the piston
is at the beginning of its stroke, and consequently the
distance between the edge Cj of the valve and the edge s
]o6 MODERN IX)COMOTIV£
of the Steam port will, in this case, be J4 inch. Through
Cj draw a straight line perpendicular to A B, intersecting
the circumference a b in in the point y; this point will
be the center of the eccentric when the piston is at the be-
ginning of its stroke, and since it is assumed that the cir-
cumference a b m also represents the path of the center
of the crank-pin, the point y will also be the position of
the crank-pin when the piston is at the commencement of
its stroke. Through the points y and c draw a straight
line y x, to represent the stroke of the piston, and divide
it into 24 equal parts. Through the point J draw a
straight line perpendicular to A B, intersecting the cir-
cumference a b m in the point g, through g draw a
straight line perpendicular to 3' x, and intersecting the
latter in the point k; this point will be the point of cut-
off. If, now, the distance between the point k and 19 is
about J/^ of the space from 19 to 20, we conclude that
the piston has traveled igy^ inches from the beginning
of its stroke when the admission of steam into the cylin-
der is suppressed.
Here we see that when a valve has no lead, as in Fig.
24, the admission of steam into the cylinder will cease
when the piston has traveled 20 inches; and when the
angular advance of the eccentric is changed, as in Fig.
25, so that the valve had J4 oi an inch lead, the point of
cut-off will be igj^ of an inch from the beginning of the
VALVES AND VALVE GEARS
107
Stroke, a difference of % of an inch between the point
of cut-off in Fig. 24 and that in Fig. 25. But the lead
in locomotive valves in full gear is only about 1/32 of an
inch, which will affect the point of cut-off so very
little that we need not notice its effect upon the period
of admission, and, therefore, lead will not be taken into
consideration in the following examples.
k
rrolcIsS^
Fig. 26.
The Travel of the Valve Will Aflfect the Point of
Out-Oflf.
Fig. 26 represents the same valve and ports shown in
Fig. 24, but the travel of the valve in Fig. 26 has been
increased to 5^ inches. The point of cut-off k has been
obtained by the same method as that employed in Figs.
24 and 25, and we find that this point k coincides with
point 21. Now notice the change caused by an increase
I08 MODERN LOCOMOTIVE
of travel; when the travel of the valve is 5. inches, as
shown in Fig. 24, the admission of steam into the cylin-
der will cease when the piston has traveled 20 inches
from the commencement of its stroke, and when the
travel of the same valve is increased ^ of an inch, as
shown in Fig. 26, the admission of the steam will not
be suppressed until the piston has traveled 21 inche's.
Here we notice a difference of i inch between the two
points of cut-off. But it must be remembered that when
the travel of a valve for a new engine is to be found or
established, the point of cut-off does not enter the ques-
tion; we simply assign such a travel to the valve that
steam ports will be fully opened, or give it slightly
greater travel when the valve is in full gear. The point
of cut-off is regulated by the lap and position of the
eccentric.
In order to find the point of cut-off it is not necessary
to make a drawing of the valve, as has been done in
Fig. 25. The only reason for doing so was to present
the method of finding the point of cut-off to the beginner
in as plain a manner as possible. In order to show how
such problems can be solved without the section of the.
valve, and, consequently, with less labor, another example
is introduced.
Example. — Lap of valve is i}i inches; travel 5j4
inches ; stroke of piston, 24 inches ; width of steam port,
154 inch; find the point of cut-off.
VALVES AND VALVE GEARS IO9
Draw any straight line, as A B, Fig. 27, anywhere
on this line mark off ij4 inch, equal to the width of the
steam port. From the edge .y of the steam port lay off
in the line A B 2i point c, the distance between the points
J and c being 1% inches; that is, equal to the amount of
lap. From c as a center, and with a radius equal to half
the travel, namely, 2^ inches, draw a circle ahm; the
circumference of this circle will represent the path of
the eccentric, and also that of the crank-pin. Through
s draw a straight line ih perpendicular to A B; this line
i h will intersect the circumference abm in the points
y and g. Through the points y and c draw a straight line
yx; the diameter yx will represent the stroke of the
piston. Divide yx into 24 equal parts; through the
point g draw a straight line g k perpendicular to y x, and
intersecting y x in the point k, and this point is the point
of cut-off. Since k coincides with the point 18, it follows
that the piston had traveled t8 inches from the begin-
ning of its stroke when the flow of the steam into the
cylinder ceased.
Now we may reverse the order of this construction
and thus find the amount of lap required to cut off steam
at a given portion of the stroke.
Example. — Travel of valve is sYa inches; stroke of
piston, 30 inches; steam to be cut off when the piston
no
MODERN LOCOMOTIVE
has traveled 22 inches from the beginning of the stroke ;
find the lap.
Draw a circle ab m whose diameter is equal to the
travel of the valve, viz., 5^. Through the center c
draw the diameter y x. In Fig. 28 we have drawn the
line y x vertically, which was done for the sake of con-
venience; any other position for this line will answer
•I*
Fig. 2T. Fig. 28.
the purpose equally well. The circumference ahm rep-
resents the path of the center of the eccentric, also that
of the crank pin; the diameter yx will represent the
stroke of the piston, and, therefore, is divided into 30
equal parts. The steam is to be cut off when the piston
has traveled 22 from the beginning of the stroke, there-
fore, through the point 22 draw a straight line gk per^
pendicular to y x, the line g k intersecting the circumfer-
ence a b m in the point g. Join the points y and ^ by a
straight line. Find the center s of the line y g, then.
k
VALVES AND VALVE GEARS III
through J and perpendicular to the line y g, draw the
line A B; if the latter line is drawn accurately it will
always pass through the center c. The distance between
the points s and c will be the amount of lap required, and
in this example it is 1-7/16 inch.
It sometimes occurs, in designing a new locomotive,
and often in designing stationary or marine engines, that
only the width of steam port and point of cut-off is
known, and the lap and travel of the valve is not known.
In such cases both of these can be at once determined
by the following method :
Example, — ^The width of the steam port is 2 inches;
the stroke of piston, 30 inches ; steam to be cut off when
the piston has traveled 24 inches from the beginning of
its stroke; find the lap and travel of the valve.
Draw any circle, 2is A B M, Fig. 29, whose diameter
is larger than the travel of the valve is expected to
be. Through the center c draw the diameter y x, and,
since the stroke of piston is 30 inches divide y x into
30 equal parts. Steam is to be cut off when the piston
has traveled 24 inches; therefore through point 24 draw
a straight line g k perpendicular to the diameter y x, in-
tersecting the circumference A B M in the point g. Join
the points y and ^ by a straight line; through the cen-
ter j of the line y g draw a line A B perpendicular to y g.
So far, this construction is precisely similar to that shown
112
MODERN LOCOMOTIVE
in Fig. 28, and in order to distinguish this part of the
construction from that which is to follow, we have used
M
y
%
\
^.--'
^'
79
\ fct-24 —
t:
L3O--'
a;
Fig. 29.
dotted lines; for the rest full lines will be used. It will
also be noticed by comparing Fig. 29 with Fig. 28 that,
if the diameter A B had been the correct travel of valve,
then c s would have been the correct amount of lap. But
VALVES AND VALVE GEARS II3
we commenced this construction with a travel that we
knew to be too great; hence, to find the correct travel
and lap, we must proceed as follows: Join the points
B and y. From s towards B, lay off on the line A B a.
point b; the distance between the point s and b must
be equal to the width of the steam port plus the amount
that the valve is to travel beyond the steam port, which,
in this example, is assumed to be % of an inch. There-
fore the distance from s to b must be 2% inches. Through
b draw a straight line b y^ parallel to B y, intersecting
the line y g in the point y^. Through the point v* draw
a straight line y^ x^, parallel to the line y x, and intersect-
ing the line A B in the point c^. From c^ as a center,
and with a radius equal to c^ b, or ca y^^ describe a circle
a b y2. Then a b will be the travel of the valve, which, in
this case, is 7^ inches, and the distance from c^ to s
will be the lap, which, in this 'example is 1-11/16 inches.
The Events of the Distribution of Steam.
The outside edges d and ca of the valve, and the out-
side edges and 02 of the steam ports, will regulate the
admission and suppression of steam; the inner edges i
and u of the valve and the inner edges s and ^2 of the
steam ports control the release and compression of steam.
The parts of the stroke of the piston during which these
events will happen can be found by the following
methods :
114
MODERN LOCOMOTIVE
Example. — Travel of valve, 5 inches ; lap, i inch ; lead,
% of an inch ; stroke of piston, 24 inches ; no inside lap
or clearance. Find at what point of the stroke the admis-
sion, suppression, release, and compression will take place.
In Figs. 30, 31 and 32 the valve occupies different posi-
tions, but the sections of the valve in these figures are
exactly alike, because they represent one and the same
Fig. 30.
valve. In Fig. 30 the distance between the edge c,
of the valve and the edge of the steam port is j4
inch, which is the amount of lead given in our example;
hence, this position of the valve indicates that the piston
is at the beginning of its stroke, and the angle mcy is
the angular advance of the eccentric. In Fig. 31 the edge
c of the valve and the edge of the steam port coincide,
and, since the valve is moving in the direction indicated
by arrow 2, the suppression commences, or, in other
words, the valve is cutting off steam when it is in the
position as here shown. In Fig, 32 the inside edge i of
VALVES AND VALVE GEARS Il5
the valve coincides with the inner edge s of the steam
port, and, since the valve is moving in the direction in-
dicated by arrow 2, the release must commence when
the valve arrives in the position here shown.
In Figs. 30, 31 and 32 the distances from the outside
edge of the steam port to the center c of the circle
Fig. 31.
a b m are equal ; that is, the points c and are one inch
apart, which is the amount of lap. The diameters of
the circles abm are all five inches, which is the travel
of the valve given in the example, and the circumference
of each circle represents the path of the eccentric, and
also the path of the center of the crank-pin. The point
y in these figures represents the position of the center
of eccentric when the piston is at the beginning of its
stroke. The distance beiween the point y and m is the
same in all figures, and consequently the angles formed
ii6
MODERN LOCOMOTIVE
by tlie lines y x and m c are equal and represent the angu-
lar advance of the eccentric.
When the valve occupies the position as represented
in Fig. 30, the center line of crank will coincide with the
line A B ; and since the piston will then be at the begpn
ning of its stroke it follows that the line A B will indi-
cate the direction in which the piston must move In
r^
Fig. 32.
order to compare the relative position of the piston with
that of the valve with as Httle labor as possible, we shall
assume that the direction in which the piston moves is
represented by the line y x, instead of the line AB;
hence the point y will not only show the position of the
center of the eccentric, but it will also indicate the posi-
tion of the center of the crank-pin when the piston is
at the commencement of its stroke. If these remarks are
thoroughly understood, there will be no difficulty in com-
prehending that which is to follow.
VALVES AND VALVE GEARS II7
Now let US trace the motions of the valve and piston
and thus determine at what part of the stroke the events
(previously named) will take place. When the crank-
pin is moving in the direction as indicated by the arrow
marked i, Fig. 30, the center of eccentric will move
through part of the circumference, a b m, and the valve
will travel in the direction indicated by the arrow 2, thus
opening the steam port wider and wider until the end
b of the travel is reached; then the valve will commence
to return, and as it moves toward the center c, the steam
port gradually closes, until the valves reaches the posi-
tion as shown in Fig. 31 ; then the steam port will be
closed and steam cut off. To find the position of the
piston when the valve is cutting off steam, we draw
through the edge c^ of the valve, Fig. 31, a straight line
Ci g, perpendicular to A B, intersecting the circumference
a bm in the point g; through this point draw a line
perpendicular to v x intersecting the latter in the point k,
and this point k being ig% inches from 3; indicates that
the piston has traveled 19% inches from the beginning
of its stroke before the steam is cut off, and that steam
has been admitted into the cylinder during the time the
piston traveled from y to k. As the piston continues to
move toward the end x of the stroke, the valve will move
in the direction of the arrow 2, Fig. 31, and the steam
port will remain closed so that no steam can enter the
Il8 MODERN LOCOMOTIVE
cylinder or escape from it; hence the steam that is now
confined in the cyHnder must push the piston ahead by its
expansive force, but the moment that the valve reaches
the position as shown in Fig. 32 the release of steam will
commence. To find the corresponding position of piston
we draw through the edge a of the valve, Fig. 32, a line
^2 Sy perpendicular to A B intersecting the circumference
a b m in the point g. Through this point draw a line g k
perpendicular to y x, intersecting the latter in the point
k, and this point k being 22^ inches from the beginning
of the stroke indicates that the piston has traveled through
this distance when the release of steam commences. Now
notice, the steam is cut off when the piston has traveled
igYs inches, and the release of steam commences when
the piston has traveled 22^ inches, consequently the
steam is worked expansively during the time the piston
moves 3>4 inches of its stroke. The steam port will re-
main open to the action of the exhaust during the time
the piston completes its stroke and moves through a por-
tion of its return stroke. In the meantime the valve
will move to the end a of the travel and return as indi-
cated by arrow 4, and the moment that the valve again
reaches the position shown in Fig. 32, the release of
steam will be stopped. To find the corresponding posi-
tion of the piston, draw through the edge d of the valve,
Fig. 32, a straight line c^ m perpendicular to A B, inter-
VALVES AND VALVE GEARS II9
secting the circumference abm in point m. Through
this point draw a straight line m h perpendicular to
yx, and intersecting the latter in the point h. Since
the distance between the points x and h is 22^ inches,
it follows that the piston has moved through 22^ inches
of its return stroke, by the time that the release of steam
will cease. As the valve continues its travel in the direc-
tion of arrow 4, Fig. 32, the steam port will remain
closed until the edge a of the valve coincides with the
outer edge o of the steam port, and during this time
the steam which remained in the cylinder is compressed,
but as soon as the edge c^ of the valve passes beyond the
steam port edge 0, the admission of steam into the cylin-
der will commence. To find the corresponding position
of the piston, draw through the outer edge o of the
steam port, Fig. 30, a straight line o g perpendicular to
A B, and intersecting the circumference ab in in the point
g; through this point draw a line g k perpendicular to
yx, intersecting the latter in the point k, and since the
distance between the points x and k is 23% inches, we
conclude that the piston has moved through 23^^ inches
of its return stroke before the admission of steam will
begin. Here we see that steam will be admitted into
the cylinder before the return stroke of the piston is
completed, and that is the object of lead, as has been
stated before. Notice once more: the compression of
120 MODERN LOCOMOTIVE
steam will commence when the piston has traveled 22%
inches of its return stroke, and will cease when the
piston has traveled 2^}i inches of its return stroke, hence
the steam is compressed during the time that the piston
travels through ij^ inches.
In each of these figures the point g represents the
relative position of the center of eccentric to that of the
valve. The point g will always be found in the circum-
ference ab m and in a straight line c^ g drawn perpendicu-
lar to A B, the former passing through the outer edge
Ci of the valve.
The reason why the point g should in all cases be
found in the straight line Cj S drawn through the outside
edge C2 of the valve is this: the center c of the circle
a h m has been placed on the line A B m such a position
(as shown in these figures), that the distance between
the center c and the outside edge o of the steam port
is equal to the lap, therefore the center g of the eccentric
and outer edge fo of the valve will always lie in the
same straight line drawn perpendicularly to A B. If the
distance between c and the outer edge of the steam
port is greater or less than the lap, then the center of
the eccentric and outside edge of the valve will not lie
in the same straight line drawn perpendicular to the
line A B, Here, then, we can conceive the necessity of
placing the center c of the circle a b m in the position
VALVES AND \
as shown in these figures. The correctness of these re-
marks must be evident to the reader if the explanations
Compress^ion
commences.
in the previous examples have been understood. Again,
since we have assumed that the point g not only repre-
sents the center of the eccentric, but also the center of
the crank-pin, it follows that, in order to determine how
122 MODERN LOCOMOTIVE
far the piston has moved from the beginning y of its
stroke when the crank-pin is at g^ we must draw a
straight line through the point g perpendicular to y x,
as has been done in these figures.
From these constructions we can obtain our answer
to the example illustrated by Fig. 31, namely:
Steam will be cut off, or, in other words, suppression
will commence when the piston has traveled 19% inches
from the beginning of its stroke, and steam will be
admitted into the cylinder during the time that the piston
travels through this distance. The steam will be released
when the piston has traveled 22^ inches from the begin-
ning of its stroke, consequently the steam will be worked
expansively during the time the piston travels through
3^4 inches. The release of steam will continue until
the compression commences, which will occur when the
piston has traveled 22y^ inches of its return stroke. The
compression will cease, and the admission of steam com-
mence, when the piston has traveled 23% inches of its
return stroke.
The same answer to our example could have been
obtained with less labor by a construction as shown in
Fig. 33, which is nothing else but a combination of the
three preceding figures ; the methods of finding the differ-
ent points in Fig. 33 have not been changed, and there-
VALVES AND VALVE GEARS
123
fore an explanation in connection with this figure is un-
necessary.
The Allen ^de Valve.
The Allen ported valve, which is sometimes referred
to as the Trick valve, is, in general design, similar to
the plain D slide valve, with the exception that it has a
passes over and through the crown forming the exhaust
arch which ends in the two ports in the valve face, as
shown in Fig. 34.
The Allen valve was designed to overcome the defects
of the plain slide valve, which does not permit the use
of full boiler or steam chest pressure at the beginning of
a stroke, when it is most needed, without giving excessive
lead, which would produce a premature cut-ofif and other-
wise impair the operation of the valve. The Allen valve
124 MODERN LOCOMOTIVE
was also designed to give a larger area for the admission
of steam, and for a portion of the valve travel the area
of steam port opening to the cylinder is, in fact, doubled.
The valve and seat are so arranged that they give two
openings to steam for the same amount of movement
necessary for a plain slide valve to give one opening;
that is, there is the same amount of opening for live
steam with one-half the travel of a plain slide valve.
As soon as the outside edge of the valve begins to open
the steam port, the supplementary passage also begins
to receive steam, thereby giving a double opening for the
admission of steam. As the travel of the valve is always
short, when an engine is running at high speed, the ad-
vantage of the double opening is evident, because it ad-
mits the steam at the beginning of the stroke, and main-
tains a full pressure on the piston till the point of cut-off.
Fig. 34 shows the valve in central position upon the
valve seat, and, the reader will observe, both steam ports
are completely closed, the same as with the plain slide
valve. Therefore the points of release or of compression
will not be affected unless the lead is changed, when
they will take place earlier or later in the stroke.
Fig. 35 shows the same valve moved off of its central
position and the reader may note that one of the steam
ports is receiving steam from each side of the valve at
the same time. It may also be observed that the steam
VALVES AND VALVE GEARS
125
edge of the valve and edge of the supplementary port
open simultaneously, and, therefore, must cut-off at the
same time.
The chief advantage derived from the use of this valve
is at high speed when the engine is worked at a short
cut-ofF, the advantage secured results from the increased
Fig. 35.
admission of steam into the cylinder, thus enabhng the
engine to develop increased power.
It has been claimed by many men in positions to know
the facts that a saving of coal amounting to about seven
per cent is obtained by the use of this valve, while
others in just as good positions to know do not consider
that this valve gains anything along economical hnes.
One undesirable feature of the valve is the fact that
when operated at short cut-offs there is double the port
126 MODERN LOCOMOTIVE
area for admission that there is for exhaust — ^because the
auxiliary port is used only for admission.
While the value of this valve has always been more
or less a debatable question, it has often been condemned
where the evil results could more properly be attributed
to its improper adjustment or application.
The best results can only be secured from the use of
this valve by designing the ports and bridges so they
will exceed the full travel of the valve by at least }i
inch. It may also be said that full advantage cannot
be obtained if the valve is given as much lead as a plain
slide valve.
The rule providing that lead should be reduced in pro-
portion to the length of the port must be modified for
the Allen valve, and the lead must be further reduced
to about one-half that given to plain slide valves. It may
also be noted here that the Allen valve should be given
enough exhaust clearance to permit a proper exhaust
period, due to the fact that at short cut-offs there is
double the port area for admission that there is for the
exhaust, and without exhaust clearance the compression
may become excessive.
The original design of the Allen valve proved im-
practicable when used as a slide valve for locomotives,
until it was balanced, for the excessive pressure bearing
VALVES AND VALVE GEARS 1 27
against its frail shell-like form caused a springing of the
valve face and rapid wear of the valve and its seat.
We will have occasion to refer to this valve again when
we reach the subject of Balanced valves.
The mUer SUde Valve.
The Miller slide valve was designed to provide a
valve which would automatically position itself on its seat
with respect to the ports.
It will be observed by referring to Fig. 36, that con-
ical stops are provided for the movement of the valve
on its rod, and, as a result, when the valve travels a
predetermined distance up the bevel, or incline, of the
cone, upon the abrupt stop of the rod to begin its return
stroke, it acts as a cushion for the valve to receive the
impact resiliently, thus preventing injury to the flanges
at the valve ends, and also preventing the stripping of
the threads on the valve rod. Another feature of the
valve is that of balancing or suspending it from the
cones, in order to prevent it from dragging on its seat,
whereby it will neither cock, stick nor blow.
The valve is of the D slide valve type, with a longi-
tudinal bore a through the valve, the ends of which
are outwardly flared, as shown at b. A valve rod c
extends through the bore a and a little beyond the outer
end of the valve; and is screw-threaded, as shown at d,
for a length exceeding that of the valve.
128 ' MODERN LOCOMOTIVE
Threaded on the portion d of the valve rod c, at the
inner ends of the valve, are cones e and f, having in-
tegral fianges g and h thereon, beyond which arc angu-
lar nuts » and m, also integral with the cones, and jain-
niUs o and p on the rod, adapted to be jammed against
the angular portions i and m of the cone e. It may also
be seen from the ilhistration that the inner diameter of
the cones ap])roximate the diameter of the bore a, the
I I
Fig. 36.
cones being beveled at the same angle as the bevel of the
valve. This valve was patented April 20, 1915, by Mr.
John W. Miller, of Rantoul, 111.
Power Required to Move a Valve.
To determine the power required to move a valve,
multiply the area of the valve face by the steam pressure
upon it, and then deduct one-third for back pressure
from steam port and exhaust port. Friction between
two smooth surfaces well lubricated varies from l/io
VALVES AND VALVE GEARS 1 29
to 1/14 of the pressure; the weight of the valve itself
being so slight that it need not be considered.
As an illustration, let us refer to a valve 10 ins. by
20 ins. with 165 lbs. of pressure per sq. in. Then
10X20^200X165=33,000 from which deduct one-third,
and the result is 22,000 lbs. This amount, if divided
by 10, will be 2,200 lbs. ; the amount of power in pounds
which is required to move the valve. This strain on the
valve gear will cause it to wear rapidly. This amount
is decreased by the proportions of the reverse lever, in
proportion to the distance between the lower connection
of the reverse lever and the point at which the reach
rod is connected to the lever, in comparison with the
distance to the end of the lever. Yet the effort re-
quired of the engineer, in moving such a valve, is very
great.
130 MODERN LOCOMOTIVE
BALANCED VALVES.
The plain slide valve used in the early days of loco-
motive construction answered all purposes then required,
but with the increase in size of the locomotive, to-
gether with the increased boiler pressure, it was almost
impossible for an engineer to reverse an engine, and a
great deal of power was wasted in moving a valve of
this kind on account of the enormous pressure on the
back of the valve.
History.
We have no doubt the problem of removing the exces-
sive pressure from the back of the valve challenged alike
the skill of practical mechanics and the professional en-
gineers of early days, and we presume many devices
were constructed to accomplish the purpose, but the first
patent issued by the United States Government covering
a balanced halve was granted to Mr. Hiram Strait, of
East Nassau, N. Y., on June 25, 1834, and the second
patent was secured by Mr. John Kirkpatrick, of Balti-
more, Md., on July 10, 1834, but neither invention
proved to be of practical advantage.
The oldest form of balance valve, which was found
to be practicable, was invented by Mr. George Richard-
son, of Springfield, Mass., and he secured a patent cov-
ering the same on October 28. 1862.
VALVES AND VALVE dEARS I3I
We are unable to say exactly when or where the
Richardson balance valve was first used, but about 1870
the Boston & Albany Railroad Company tried it out on
an engine and the results obtained were so satisfactory
that the company applied the invention to the majority
of their locomotives.
Countless other forms of balancing valves have made
their appearance and have departed since, but we shall
confine our discussion to the various types which have
stood the test and which have been found to be prac-
tical, together with a few new inventions which may
demonstrate their worth later on.
Object of Balancing.
Almost all forms of balancing slide valves are con-
structed on the same principle, and are intended to
prevent the steam chest pressure from exerting its force
on the greater portion of the back, or upper surface, of
the valve; thus enabling the valve to be easily moved,
without excessive friction on the seat or excessive effort
to lift it against the pressure which holds it down.
A slide valve may be considered balanced when the
pressure on its top is just enough in excess of the
pressure under it to insure the valve remaining on its
seat, but not sufficient to prevent the valve from re-
lieving excessive pressure, or accumulation of water, in
the cylinder.
132 MODERN LOCOMOTIVE
In the design of the valves, the balance is equally as
important as the efficient distribution of steam in the
cylinders, for an improper, or defective, balance will im-
pose enormous stress upon the valve gear and connect-
ing rods, and greatly impair the work they are required
to perform.' In fact it is necessary for the designer to
consider, when calculating the dimensions of stems and
rods, the increased work that would be imposed upon
them in the event of an accident to the balancing strips
and lubricating apparatus.
Area of Balance.
The size and shape of the protected area on the top of
the valve varies in different forms of balancing, but it
should equal the sum of the area of one steam port, the
exhaust port, and two bridges, plus eight per cent of
this sum for plain valves, and plus five per cent for
Allen-ported valves. The balanced area should be meas-
ured from the outside of the strips, or the bottom out-
side edge of the inner ring when the outer ring is
raised.
It may be said generally that good results may be ob-
tained if about 65 per cent of the opper surface of the
valve is protected, and 35 per cent exposed, to counteract
the upward pressure of the steam against the face of the
valve, which is not at all times uniform.
VALVES AND VALVE GEARS 133
Methods of Balancing.
The original method of balancing a slide valve, which
was first employed by Richardson, is generally followed,
and the object is accomplished by fitting four iron strips
J4xij4 inches, which are called balance, or packing,
strips, in suitable grooves cut in the top of the valve
near its outer edges, thus forming a rectangular enclos-
ure on top of the valve. The strips are supported on
coil or semi-elliptic springs to hold them against the
pressure plate which is attached to the cover of the
steam chest.
A later form of balancing consists of a conical ring
cut through at one point, and fitted to a taper bearing
on the top of the valve. No springs are necessary to
support the ring since its reaction on the taper bearing,
due to its elasticity and the steam pressure, tend to lift
it against the pressure plate.
Hole in Top of Balanced Valve.
One or more small holes are drilled through the top
of balanced valves to permit any small volume of steam
which might get on top of the valve, as a result of de-
fective balance strips, to pass into the exhaust and
thence to the atmosphere, in this manner maintaining
the balance feature of the valve. This hole in the top
of the valve is generally referred to as the release port.
134 MODERN LOCOMOTIVE
If an escape for the steam which leaked by the bal-
ance strips was not provided, such steam would, in
time, accumulate on the top of the valve, and neutralize
the benefits secured from properly balanced valves.
AdvButages of Balancing.
The chief advantage of a balanced slide valve is the
fact that it is easily moved, without excessive friction,
and that it can relieve itself of excess pressure, or the
accumulation of water in the cylinder, by lifting from
its seat. As a result it is unnecessary to provide means
for relieving excess pressure in the cylinders.
Disadvantages of Balanced Valves.
When cylinders of large dimensions are used, with
high steam pressure, the slide valve becomes unduly
large for a proper length of port opening and, even when
the valve is well balanced, creates an excessive amount
of friction when it is moved on its seat. A slide valve
when used on a very large cylinder gives undue cylinder
clearance due to the increased length of the ports, and
the large steam chests necessary, and causes more or
less steam condensation. This probably accounts for
the high water rate of engines with very large valves
and steam chests.
Another objection often advanced is that the end strips
cut into the balance plate, and therefore, it is uncom-
VALVES AND VALVE GEARS 135
mon for a locomotive to run more than 25,000 miles
before the valves require refacing. This difficulty may,
however, be overcome by dispensing with springs under
the front and back strips, by allowing the end strips to
overlap and receive their support from the long side
strips. When such an arrangement is used shoulders
should be provided on the bottom of the side strips so
that they cannot work out of their proper positions.
While slide valves have been operated successfully
with a high degree of superheat, they are not as reliable
as the piston valve under high temperature steam.
The Richardson Balanced Slide Valve.
The Richardson balanced valve, briefly referred to
heretofore, is similar to the plain slide-valve, but it has
a certain amount of space on the top of the valve en-
closed by four rectangular packing,- or balance, strips,
yixij/i inc'hes, of cast iron, which are held tightly
against the pressure plate by the steam pressure, and by
semi-elliptic springs placed in the grooves beneath them.
The two shorter packing strips have gib-shaped ends
to retain them in their proper positions, and are arranged
so that no packing strip of the balance device will travel
over, or rub, ihe path of travel of any other strips, there-
by insuring a steam tight joint at various travels. The
balance strips are marked p p on the illustration. Fig. 37.
136
MODERN LOCOMOTIVE
There is also provided a pressure plate, A, which is
bolted to the inside of the cover of the steam chest, but
this may be cast in a single piece. The steam acts
against the outside of the strips, making them steam
tight, and, as a result, excludes steam from the top of
the valve. A small amount of clearance between the
valve and the pressure plate is allowed, so that excessive
Fig. 37.
cylinder pressure may be relieved by allowing the valve
to lift slightly from its seat. A small hole, h, is drilled
through the top of the valve, so that any steam that es-
capes past the packing strips may pass out to the exhaust
without exerting pressure on the top of the valve.
The proper area to be enclosed within the four balance
strips may be determined by adding the area of the ex-
haust cavity to the area of one steam port. If a greater
area be enclosed there is danger of overbalancing the
valve, and a smaller area will often give satisfactory
results.
• •*•► «
VALVES AND VALVE GEARS
137
The reliability of this type of balanced valve, together
with its simplicity of construction, and the fact that
the balance feature can be used with various forms of
slide-valves, have resulted in its general adoption, and
it is now used extensively.
The AUen-Richardson Balanced Valve.
This well known type of balnnced valve is simply a
combination of the Allen ported valve and the Richard-
FiG. 38.
son system of balancing, which is shown in the sectional
view presented in Fig. 38.
We pointed out in the preceding pages, when analyz-
ing the Allen valve, that it was not practical for loco-
motive work, until it was balanced, but when used in
connection with the Richardson system of balancing it
gives very good results, and thousands of this combina-
tion type are now in service.
138
MODERN LOCOMOTIVE
American Balance Valve.
This form of balance valve is used quite extensively in
locomotive service, and its popularity is, no doubt, due
to its simplicity of construction, positive action, economy
of maintenance, and large area of balance.
The valve is balanced by a single or double cone, or
disk, cast on the back of the valve, the single cone being
Fig. 39.
preferable where steam chest space will permit its use.
These cones have a beveled face, are fitted on the outside
by taper rings, marked R in the illustration. Fig. 39, of
the same bevel as the cone rings, made J^ inch smaller
than the bevel of the cone, and are expanded over the
cone so that it does not require a spring.
The conical ring is cut through at one point, in order
that the ring may expand, and the opening is protected
by an L-shaped plate of the same depth as the ring, which
fits against the cone and insures a steam tight joint.
VALVES AND VALVE GEARS 139
Owing to the natural elasticity of the ring and its ex-
pansion over the cone, a tension is placed on the ring,
the function of which is to close the ring on the cone,
which necessarily moves upward. The ring is therefore
self-supporting and self-adjusting.
For the valve to lift from its seat it is necessary to
force the cone up into the taper ring; and since the ring
is held, by the steam chest pressure, from opening, the
valve cannot lift without first overcoming the entire fric-
tion of the beveled face, besides opening the ring against
the steam chest pressure. Of course, if the taper was
made large enough, say 45 degrees, the action of the
steam chest pressure on the circumference of the ring
would wedge it between the cone and the steam chest
cover and, as a result, exert an enormous pressure on
the valve, so that it would not work satisfactorily. Ex-
tensive experiments, however, have been made, with the
taper from 9 to 24 degrees, and, from actual tests, the
proper degree of taper has been ascertained whereby
the ring will rise under all conditions without crowding
the balance plate more than is necessary to give good
results.
The rings are made of hard close-grained cast iron
from standard gauges, which are fitted on the lathe in
place of a caliper, or rule, and as they are made i inch
deep, they can easily wear ^ inch and still adjust them-
140 MODERN LOCOMOTIVE
selves. As the ring is turned J4 ii^ch smaller than its
working diameter, it can be readily seen that 1/32 inch
in the diameter of the ring either way from the size speci-
fied would not in any wise interfere with the service of
the valve.
The rings are all bored smaller than the diameter at
which they are to work; therefore when a ring is set
on its cone it will stand higher than in its working posi-
tion. The face of the pressure plate must not be closer
than ys inch to the top of the cone after the steam chest
cover has been screwed down, for, in placing the steam
chest cover in this position, the ring is expanded over
the cone until its inside diameter at the bottom is the
proper balancing diameter.
Sufficient allowance must be made for the removal of
the valve-yoke, and, as a result, a detachable disk is used,
but the makers recommend an arrangement whereby the
valve-yoke may be carried on the steam chest at the ends
of the valve.
When the valve is in position, and the steam chest
cover has been bolted down, there must be }i inch space
between the face of the upper bearing (in this case
the pressure plate), and the top of the disk, or cone.
This arrangement will allow the valve to lift from its
seat }i Jnch, which it will do as soon as steam is shut off
VALVES AND VALVE, GEARS I4I
while the engine is in motion, if it is not held down
by the. valve-yoke.
A casual inspection of the illustration may lead the
reader to believe this valve is overbalanced, but the im-
pression will disappear when proper consideration is made
for the reaction from the surface of the bevel ring, and
friction of the conical joint.
This design of balance valve was invented May 3, 1892,
by Mr. W. J. Thomas, of Sausilito, Cal., and the im-
proved rings were patented June 21, 1898, by Mr. John
T. Wilson, of Jersey Shore, Pa. The valve is manu-
factured by The American Balance Valve Company of
Jersey Shore, Pa.
Gould Balance Valve.
The Gould balance valve was designed to overcome
the tendency of balance valves, when slightly worn, to
suffer from steam leakage ; and also with the idea in view
of obtaining a valve that will take up its own wear, so
that this difficulty is very largely overcome.
This valve is constructed like the plain D slide valve,
with the same face measurements, and it is intended to
work on the same ports and has the same admission,
cut-off and release as the common D slide valve. Fig. 40
shows this valve with cover displaced and rings raised.
142 MODERN UDCOMOTIVE
This valve is semi-circular or half round in shape, and
the flat portion travels on the valve seat ; while in opera-
tion it travels under a half round, or semi-circular, pres-
sure plate which rests on the valve seat ; it has expansion
half rings, four in all, two at each end of the valve,
and these rings expand, with steam, against the pressure
Fig. 40.
plate, thus preventing steam from entering or escaping
at each end of the valve.
Between these rings at each end is a groove of exactly
the same length as the packing grooves and it extends
around the oval portion of the valve ; when the rings
are expanded this groove becomes a steam chamber, as
steam is taken from the ports in passing over them,
through holes bored in the face of the valve to this'
VALVES AND VALVE GEARS I43
chamber or circular groove. The semi-circular pressure
plate keeps the steam from pressing downward upon the
back of the valve proper; the valve is balanced against
port pressure by steam taken from the ports through
to the chamber previously described ; the pressure plate
is kept from moving endwise by pins in each end of
the plate which rest against the walls of the steam chest,
Fig. 41.
and is held down firmly by a set screw through the steam
chest cover.
An X-ray view of the valve through its semi-circular
casing, showing its interior construction, and the sleeve,
or valve rod connection, is presented in Fig. 41.
The advantage of the Gould valve is that there is no
boiler pressure on the back of the valve, as the cover
fully protects the valve from live steam, and the rings
exclude the steam from passing beyond the ends of the
valve, as there is no opening for steam to get between
144 MODERN LOCOMOTIVE
the cover and the valve. The ends of the valve are ex-
posed to live steam; but, the pressure on both ends being
equal, there is no end friction. The communicating ports
always allow the same pressure on the back of the valve
that is on the face of the valve, thus keeping it perfectly
balanced at all times. This valve is manufactured by the
Gould Balance Valve Company, of Kellogg, Iowa.
The Mewes Valve.
Several novel features are presented in a valve pat-
ented May 22, 1 91 7, by Mr. Richard W. Mewes, of Des
Moines, Iowa, so we believe a detailed description of
the same will be of interest to the reader.
After stating that the object of the invention is to
provide a valve of simple, durable and inexpensive con-
struction, for engines, particularly locomotives, the in-
ventor claims the desired result is attained in the con-
struction and arrangement of the various parts of the
device, as shown in the accompanying illustrations,
which he describes as follows:
Fig. 42 shows a top, or plan view of the steam- chest
with my improved valve therein, the top or cover of
the steam chest being removed.
Fig. 43 shows a vertical, sectional view, taken on the
line 2 — 2 of Fig. 42.
Fig. 44 shows a top, or plan view of one end of my
valve with the cover plates 34 and the plate 39 removed
VALVES AND VALVE GEARS
145
for the purpose of illustrating other parts of the inven-
tion.
Fig, 45 is a detail, perspective view of part of the
packing and balancing mechanism at the upper part of
the valve.
Fig. 42.
Fig, 46 is a front elevation of a portion of the front
end of the mechanism shown in Fig, 45, showing the
manner in which the two packing plates or strips are
arranged at right angles to each other and joined, and
Fig. 47 shows a vertical, sectional view taken on the
same line as Fig. 43, but enlarged for the purpose of
clearness, and showing only a small part of the valve.
In the accompanying drawings, I have used the refer-
ence numeral 10 to indicate generally the steam chest of
146 MODERN LOCOMOTIVE
a locomotive engine, having the intake ports 11 arranged
in the bottom of the steam chest near the ends thereof,
and having the main exhaust port 12 preferably in the
center of the bottom of the steam chest and having the
ports 13 arranged on opposite sides of the port 12 for
steam from the opposite ends of the cylinder.
Fig. 43.
The portion of the bottom of the steam chest forms a
valve seat 14. Arranged to slide on the seat 14 is a
sliding valve, having a main central body portion 15.
operatively connected with which is the valve stem 16,
slidably extended through the side of the steam chest.
In the lower central portion of the body 15 of the valve
is a recess 17 adapted at all times to be in communica-
tion with the port 12. and adapted in different positions
of the sliding movement of the valve also to be selec-
tively in communication with the ports 13.
VALVES AND VALVE GEARS
147
Formed on the lower portion of the valve body are
opposite lateral extensions 18, which, at their outer ends,
are thicker than the intermediate portions of said exten-
sions 18, as shown in Fig. 43. Formed in the extensions
18 between their ends and the body 15 are ports 19.
n
O O'^^O
Fig. 44.
The right-hand port 19 on the left-hand movement of
the valve is adapted to register with the right-hand
port 13, and the left-hand port 19 is adapted in the
right-hand movement of the valve to register with the
left-hand port 13.
In the upper portions of the outer ends of the exten-
sions 18 are recesses 20 in which I preferably mount
148 MODERN LOCOMOTIVE
suitable material 21% such as waste or the like, for col-
lecting, holding and distributing a lubricant.
Extending downwardly from the lower parts of the
recesses 20 is a plurality of small passages 21 whereby
a lubricant can pass downwardly from the recesses 20
to the lower surfaces of the extensions 18. The lower
surfaces of the extension 18 are provided with grooves
Fig. 45.
22, for connecting the lower ends of the small pas-
sages 21.
The upper portion of the outer ends of the extensions
18 are preferably covered with a screen or the like, 23.
The recesses 20 do not extend to the ends of the exten-
sions 18.
Resting above the screen are frames, 24, adapted to be
secured to the extensions 18 by means of screw-threaded
VALVES AND VALVE GEARS 149
bolts 25, having in them openings 26 registering with
the opening 2^ extending downwardly through the ends
of the extensions 18, whereby a lubricant can pass
through the screws downwardly through the extensions
18. The central portions of the frames 24 are cut away
at 28 to admit the lubricant from the steam chest to the
screen 23, and therethrough to the material 21^ and the
passages 21.
Before describing the structural features of my im-
proved valve whereby it is balanced, I will explain the
operation and advantages of the extensions 18.
D valves of the type used in locomotive engines are
ordinarily constructed without such extensions, and with
portions which extend as far as the inner walls of the
passages 19. It will thus be seen that in the ordinary
D valve there are no passages 19, but steam in the
different positions of the valve passes downwardly past
the sides of the D valve into the ports 13. It is well
known that in D valves there is a pressure, at certain
times, upwardly on the sides of the valve, so that the
valve tends to have a rocking motion, whereby the
corners of the valve at 29 tend to become worn and
rounded, and therefore the valve is not tight, and leaks
steam. This is an objectionable feature of the ordinary
D valve, which is well known, and it is one of the prin-
cipal objects of my invention to construct a D valve in
150 M0DE8N LOCOMOTIVE
such form as to overcome this objection by preventing
the rocking movement and by taking off the wear of
the corners 29. This purpose is partially accomplished
by the construction hereinbefore described, and par-
tially accomplished by the construction whereby the valve
Fig. 46. Fig. 47.
is balanced as will be hereinafter more fully explained.
By the construction already described, and by the use
of the extensions 18, it will be seen that the lower sur-
faces of the extensions 18 beyond the passages 19 en-
gage the valve seat, so that there is no tendency for
■ the valve to rock, and the wear will be upon the corners,
or edges, ;^o, which will not cause any leakage or loss of
steam. The corners or edges 29 will remain sharp, so
that the valve will retain its efficiency.
VALVES AND VALVE GEARS 1 51
In order to secure complete and perfect lubrication
for the sliding parts of the valve and valve seat, I have
provided the means above described, including the ma-
terial 20, so that the oil will pass downwardly through
the recess 20 and the passages 21 to the surface of
the valve seat, where it will be distributed along the
groove 22, and perfect lubrication between the exten-
sions 18 and the valve seat will be maintained.
The accomplishment of such lubrication I consider
as another very important advantage of my improved
valve.
I will now describe the construction whereby my
valve is balanced. Resting upon the upper part of the
valve is a plate 31, which, as illustrated in Fig. 43, is
of considerably greater width than the body portion of
the valve. In this connection it may be stated that the
area of the projecting portions of the plate 31, including
the area of the body 15 above the recess 17, is substantial-
ly equal to the area of the valve which is subjected to the
downward pressure of steam, so that when the valve is
in operation, the upward pressure of steam will tend to
balance the downward pressure thereof on the valve to
balance the valve. The plate 31 is secured to the body
15 of the valve by means of bolts 32.
Near its side edges the plate 31 is provided with longi-
tudinally arranged grooves 33. Mounted in the grooves
152 MODERN LOCOMOTIVE
33 are upright plates 34 which may slide vertically in
the grooves 33 and are yieldingly held at the upper limit
of their movement by means of springs 35 in the bottoms
of the grooves 33.
At the upper end of each plate 34 are opposite lateral
extensions 36, clearly shown in Fig. 43, and it will thus
be seen that the plates 34 with the extensions 36 have
substantially the form of a T-iron.
In the extensions 36, on opposite sides of the plate
34,' are longitudinal slots, or openings, 37. The use of
the extensions 36 also gives a large bearing surface at
the upper end of each plate 34, so that there will be less
tendency for the plates 34 to rock and wear against the
sides or walls of the grooves 33.
Extended through the body 15 and through the central
portion of the plate 31 are passages 38, whereby any
steam which may leak past the plates 36 may pass down-
wardly to the exhaust port 12. The openings 37 afford
passages for a lubricant whereby the lower surface of
the balance plate 39, against which the upper part of the
plates 34 and the extension 36 slide, may be thoroughly
lubricated.
In the upper surface of the plate 31 are grooves 33*,
similar to the grooves 33, arranged at right angles thereto
near the outer edges of the plate 31, and in the grooves
last described are mounted plates 40, similar to the plates
VALVES AND VALVE GEARS 153
34, which at their ends fit against the plates 34, the inner
extensions 36 being cut away at their ends to allow the
ends of the plates 40 to bear snugly against the plates 34.
At their upper ends, the plates 40 are provided with a
pluraHty of opposite, laterally extending tongues 41,
which afford broad bearing surfaces, and at the same time
allow spaces for the admission of a lubricant to the
plate 39. The plates 34 and 40 are similarly mounted in
the grooves in the plate 31.
It will be understood that there is oil in the steam
passing through to the valve, so that the wearing parts
of the valve are lubricated by oil furnished with the
steam, and held in suspension therein.
In the edges of the plate 31, on each side thereof, are
horizontal openings extending from the grooves 33 and
33*, respectively, to the outer surfaces of the plates. In
the openings 42 are mounted springs 43. Outside the
springs 43 are mounted screw-threaded bolts 44, whereby
the springs 43 are held against the plates 34 and 40 for
maintaining tight joints at all times. It will thus be
seen that by means of the plate 31 my valve is balanced
and at the same time the upper moving parts are
thoroughly lubricated.
My improved valve, on account of the extensions 18
and the means for lubrication, will wear much longer
than the ordinary sliding D valve used on locomotives.
154 MODERN LOCOMOTIVE
Thus by the use of the extensions on the valve, which
overlap or travel upon the parts of the valve seat which
project beyond the passages 13, during all operations of
the valve, two vitally important purposes are accom-
plished, which are two of the main purposes of this im-
provement. One of these purposes is the affording of
the broad bearing for the lower surface of the slide valve,
whereby the ends of the valve are supported at all times
on the valve seat, and the rocking or tilting of the valve,
which is a serious defect in many slide valves, is wholly
avoided. The other purpose is to afford a receptacle for
the oil receiving material 21* which absorbs from the
steam the oil in solution therein, and furnishes lubricant
which can pass downwardly through the passage 21 for
thoroughly and completely oiling the valve seat.
The extensions, particularly when formed with the
oiling means shown, permit the oiling of the surfaces
of the valve seat which extend between the passages 13
and the extreme ends of the valve seat, by oil from the
steam in the steam chest, and also by oil passing through
passages 21. On each movement of the valve, the under
surface of the extension is lubricated bv oil in the steam,
as is clearly illustrated from the showing of the right-
hand extension in Fig. 43.
The valve seat is also lubricated by oil in the steam
which passes downwardly through the passages 19. It
VALVES AND VALVE GEARS 1 55
thus appears that the surfaces of the valve seat and the
valve are more thoroughly and continually lubricated than
could be possible with the ordinary form of valve having
no such extensions.
It is well known that in ordinary locomotives a constant
supply of oil is furnished to the steam so that when
the steam passes to the slide valve it contains oil. Where
everything is working satisfactorily oil will be fairly well
distributed over the working parts of the slide valve.
There are times, however, when the supply of oil to the
steam may be accidentally shut off, and there are also
times, as when the engine is coasting, when the slide
valves are working but no steam is being furnished
thereto and consequently no oil is being furnished to the
valve parts. By providing the recesses 20 and the waste
21* or other material in said recesses, for collecting, hold-
ing and distributing oil, I provide means for taking up
surplus oil if there should be more than enough to prop-
erly lubricate the parts, and holding it until such time
as not enough oil is furnished to saturate the waste 21*,
whereupon oil will pass from such waste as a sort of
reservoir through the passages 21. I thereby obtain a
more even and continuous and thorough lubrication than
could otherwise be done.
It is also clear that by the use of the extensions, it is
impossible for the valve and valve seat to wear convex
156 MODERN LOCOMOTIVE
and concave, particularly along the lower edges of the
valve, as occurs where the ordinary D valves are used,
insomuch as with my valve, the valve is held properly
seated at all times and the extensions prevent any rocking
of the valve. Where the ordinary D valve is used, the
valve and valve seat wear convex and concave, which
requires the re-surfacing of the valve by chipping or the
like.
In the actual use of locomotives there is, of course, a
constant leakage during the time when the valve is
deteriorating until it becomes so bad it must be repaired.
The loss due to such leakage is avoided where my valve
is t;ised.
The Miller Double Acting Slide-Valve.
A double acting slide-valve designed to embrace the
advantages derived from inside clearance, and obviate
the disadvantages resulting from excessive outside' lap,
by extending the period of exhaust and delaying com-
pression until substantially the point of admission, with-
out delaying admission or hastening cut-off, was patented
January 13, 1914, by Mr. Joseph Miller, of Chicago, 111.
The principal feature of the improvement is the em-
ployment of an auxiliary valve, sliding on and above the
main slide valve, alternately opening and closing the two
small auxiliary ports — one at each end — which extend
through the main slide valve.
VALVES AND VALVE GEARS
157
In Ing, 48 it niav be observed the main valve is moving
to the right, and the auxiliary valve is being moved in
the same direction, by special operating mechanism, and
the upwardly projectinjr portions, or biitTers, of the main
Fig. 48-
valve, against which the auxiliary valve abuts. It will
also be seen by inspection that the center exhaust passage-
ways extending vertically through the center of the main
and auxiliary valve are always in communication.
The auxiliary exhaust passages, which extend entirely
through the body of the main valve, are positioned to
register with the cylinder ports in the valve seat after
158 MODERN LOCOMOTIVE
the inside edges of the main valve have passed inwardly
beyond the ports, and delay compression by providing
means of escape for the steam which would normally
be trapped in the cylinder ahead of the advancing piston.
This is manifest by an inspection of the left-hand port
shown in the illustration, for the point of exhaust has
been reached in the right-hand port while exhaust con-
tinues in the left-hand port; in fact, the left-hand port
will remain open for exhaust until J4 i^ch of the port
opening for steam admission.
At the same time it will be seen that premature re-
lease in the right-hand port is prevented by the auxiliary
valve closing the upper end of the vertical auxiliary pas-
sageway extending through the main valve, so as to
prevent release until the inner edge of the main valve has
moved to a position to open the right-hand cylinder port.
The auxiliary valve travels back and forth in the steam
chest with, and in the same direction as, the main valve,
as the latter approaches the end of its stroke.
The two valves are balanced in the usual manner by
the use of springs, or other resilient means, interposed
beneath packing strips which fit in grooves and are forced
against the pressure plate, to produce a seal between the
interior of the valves and the live steam compartment.
The main valve is lubricated by means of steam,
trapped in a series of transverse grooves, or steam
VALVES AND VALVE GEARS 159
pockets, cut in the valve face beneath the valve, as the
latter slides thereover. The expansive force of the
trapped steam in these pockets tends to raise the valve
from its seat, thereby reducing friction and eliminating
the necessity of artificial lubrication. In fact it is claimed
that this system of lubrication permits the valve to be
used with success on a high degree superheated engine.
It has been demonstrated that one of these double act-
ing valves having i inch outside lap, and }i inch exhaust
lap, will give 40% increase of expansion. With i inch
outside lap, and exhaust line and line, however, a de-
crease of compression of about 75% over the plain slide
valve, may be obtained.
A set of these valves have been in use on an engine
of the Illinois Central Railroad Company for about three
years, and so far neither the valve nor the valve seats
have been refaced, nor has as much as a file been touched
to them. The locomotive equipped with this valve shows
a good coal and water record, leading all other engines
of her class in similar service by a good percentage, but
an official test has never been conducted, and therefore
accurate data cannot be given.
The Walsh Balanced Slide-Valve.
The valve shown in the accompanying illustration is
unlike the ordinary D shaped type in its construction,
for it is composed of two triangular end pieces, which
i6o
MODERN LOCOMOTIVE
are connected by a hollow cylinder, through which the
valve stem is projected.
The valve proper is enclosed entirely in a triangular
hood, or covering, which is held in position by a set
screw projecting through the top of the steam chest
cover.
E
f
^///////////////// ////y/////////////777777P. 5g
I
^^^^^^
Fig. 49.
Each end member of the valve is provided with a
groove in its apex, or top, extending the length of one
face, and a metal balance strip of less thickness than
the depth of the groove. A side view of this groove,
with the balance strip set in it in the position it occupies
when subject to steam chest pressure, is clearly shown in
Fig. 49.
The space, or opening, below each balance strip, and
between it and the bottom of the groove, is connected
VALVES AND VALVE GEARS l6l
by means of pin hole ports, or openings, which are
marked A and B, with steam chest pressure.
In operation, live steam from the steam chest is ad-
mitted in the grooves, beneath the metal balance strips,
through the small ports A and B, and the steam pressure
forces the metal balance strips outward and upward,
against the top and one inner face of the hood, or cov-
ering, thus equalizing the pressure of the valve on its
face and balance plate. As a -result the valve is well
balanced, for the steam admitted below the balance
strips through the ports A and B accomplishes the same
results as the springs usually employed in balanced
valves. In fact this method of balancing is more reliable
than springs, for there is no danger of a suspension in
the balance, and it will not cause the balance strip to
bear against the top or inner face of the hood, or cover-
ing except when the engine is working steam.
This valve was patented June 3, 1913, by Mr. James
P. Walsh, of Marengo, Iowa.
The Wilson Balanced Slide-Valve.
This valve was designed for high-pressure, and, as it
is of the "Grid Iron'* type, it is very light, and, being
the only moving part, the reciprocating weight is the
minimum.
It will be observed that the valve has two faces which
are parallel and of identical construction; that the lower
1 62
MODERN LOCOMOTIVE
surface of the balance plate is of the same area and
shape as the raised valve seat, that the pockets I I are
of the same area as the steam admission ports to the
cylinder; that the "floating" balance plate can rock
slightly and lift to relieve the cylinder when the engine
Fig. 50.
is drifting, inasmuch as the plate is located a short dis-
tance from the under surface of the pressure plate; and
that the packing strips are stationary.
The inner area of the top surface of the balance plate
bounded by the end packing strips and outer strips, which
is to be enclosed from the pressure of steam within the
chest, is determined in any given case by experiment.
However, the main requirement is that the area of the
VALVES AND VALVE GEARS 163
balance plate exterior of these packing strips, which is
subjected to steam pressure, should be sufficient to hold
the valve in place and allow it to move from its central
position when moderate force is applied to the valve
stem.
Fig. si.
When the valve is moved from mid-position. Fig. 50,
to the opening position. Fig. 51, steam passes directly
downward through the admission passage M to the cyl-
inder. At the same time steam passes to the enclosed
area B at the top of the balance plate. Steam pressure
upon the top and bottom faces of the valve, where it
laps the port, and the top and bottom faces of the bal-
ance plate at the edge adjacent the port, is thus equalized.
In the wide open position, Fig. 52, the balance is pre-
164 MODERN LOCOMOTIVE
served, inasmuch as the top face of the valve at the left
has passed out from under the balance plate the same
distance its lower face has passed over the edge of the
valve seat. When the valve covers the port, the
pressure upon the top and bottom faces and upon the
Fig. 52.
top and bottom surfaces of the balance plate is obviously
constant. As the valve moves farther toward the right,
and reaches the position of exhaust, Fig. 53, steam passes
directly from the port, and also by way of the exhaust
passages to the exhaust cavity. At the same time steam
in the inclosed space between the balance strips above
the port passes out into the exhaust cavity, thus preserv-
ing the balance which otherwise would be destroyed by
VALVES AND VALVE GEARS
165
the top surface of the valve excluding from steam pres-
sure the under surface of the balance plate adjacent to
the pocket therein.
The balance area varies with each stroke, or move-
ment of the valve, an amount sufficient to correspond to
Fig. 53.
the changed position of the valve on its seat at the
different points of its travel. It also provides a double
exit, and admission, for the release and admission of
steam.
This valve was patented March 9, 1909, by Mr. John
T. Wilson, of Jersey Shore, Pa., and is manufactured
by the American Balance Valve Co., of Jersey Shore,
Pa.
1 66 MODERN LOCOMOTIVE
PISTON VALVES.
The first patent issued by the United States Govern-
ment covering a piston valve was secured by Mr. M. P.
Mack, of Canandaigua, N. Y., in March, 1866, about
32 years after a patent was first issued for the balanced
valve. We have pointed out, however, that the early
balanced valves proved to be impractical, and it was not
until the year 1862 that a balanced valve of merit was
produced. We may, therefore, say, comparatively speak-
ing, that the piston valve is as old as the balanced type.
The piston valve, like the balanced valve, was not gen-
erally adopted for many years after its invention, but
there were more serious obstacles in its path than con-
fronted the early balanced valves. For example, the
piston valve was obliged to overcome the popularity of
the balanced valve which had been before the public for
some years, and had answered all requirements of the
low pressure engines then in use. The piston valve was
criticised because its use resulted in the rapid wear of
the valve cage at the port openings, which was partly
due to the absence of bridge strips in the port openings
as ring bearers for the piston. Another objectionable
feature was that the tallow used in early days for lubri-
cation prevented the piston valve from giving good re-
sults.
VALVES AND VALVE GEARS 167
In some of the earlier forms of piston valve the steam
was admitted at the outer ends of the valve and, as a re-
sult, the action of the valve, in such cases, was precisely
the same as that of the plain slide-valve. We do not
believe,, however, that any outside admission piston valves
are now in use, with the exception of a few special
types applied to existing slide valve cylinders, which will
be presented later.
After some of the objectionable features of the piston
type of valve had been eliminated, and various improve-
ments had been made in its construction, the valve was,
in time, adopted for marine engines, where it rendered
good service. As a result^ it has grown into popular
favor in locomotive construction, and is now used ex-
tensively.
The piston valve is of cylindrical form, and derives its
name from the fact that it consists of two pistons, one
to each port, which are connected by an ordinary spindle.
The valve works in a cylindrical valve seat, in which port
openings are made completely around the valve.
This arrangement allows greater port area, and re-
quires less space Tor the operation of the valve, for this
type of valve is generally made long enough to bring the
two faces, or working edges, of the valve close to the
ends of the cylinder, thereby reducing the clearance space
between the valve face and the piston.
l68. MODERN LOCOMOTIVE
This type of valve has been well described, by numer-
ous authors, as an ordinary slide valve with its plane sur-
face and rectangular steam ports rolled into cylindrical
form, and we are willing to adopt this definition as satis-
factory.
General Design.
As a general rule the piston valve is made hollow,
with as large a passage through the center as possible,
to secure a large area for the exhaust at the instant re-
lease occurs, so that the back pressure will be reduced
to a minimum. The exhaust produces more or less pres-
sure on the end of the valve rod and, as a result, the
follower ribs of the valve should have a long bevel.
The idea that the effect of a contracted exhaust nozzle
is more apparent, and detrimental, with the piston type
of valve than with a slide valve, is erroneous, and may
be explained by directing attention to the fact that back
pressure from the exhaust acts on the outer ends of the
piston valve, and, as the result of short ports, it exerts
more force on the pistons.
The Built-Up Type.
The most common type of built-up piston valve is con-
structed of two follower plates made of cast steel or
malleable iron, two cast iron skeleton or bull rings, and a
single connecting piece called a spool.
VALVES AND VALVE GEARS 169
The Solid Type.
As a general rule the solid type of piston valve is now
made hollow, and is supplied with three light section
snap rings — ^about % by J^-inch — on each end. From an
economical standpoint the solid type is preferable, for it
can be manufactured and maintained at lower cost, but
in case of an accident the entire valve must be replaced,
while a renewal of the damaged part is all that is neces-
sary with the built-up type of valve.
Size of the Piston Valve.
There is a great difference of opinion regarding the
proper size of the piston valve that will give the best re-
sults for large high pressure, engines, but the prevailing
opinion at present appears to be, that the circumference
of the valve, minus the space occupied by the bridges,
must, to a considerable extent, exceed the length of the
sHde-valve port for a similar bore of cylinder. This is
accounted for by the resistance offered by the bridges,
and by the fact that the portion of the port diameter oppo-
site the cylinder cannot be so effective as that nearest it.
The port ordinarily should be so proportioned that the
area around the outside of the bushing at any point is
equal to the combined area of all openings above this
point. Formerly the use of a piston valve 55 per cent
of the diameter of the cylinder was considered good prac-
170 MODERN LOCOMOTIVE
tice, but of late there has been a tendency toward a
smaller diameter of valve, and it has been demonstrated
that a 12-inch diameter is large enough for cylinders up
to 2^ inches in diameter.
The size of the valve can be changed by increasing
or decreasing the thickness of the valve bushing, and it
is evident that a reduction in the size of the valve will
reduce its weight and its stress on the valve motion,
especially at high speed.
Without doubt, it is possible to use a smaller diameter
of valve with superheated steam than with saturated
steam, and this is probably due to the fact that the
velocity of superheated steam through the ports is much
greater.
The only point of similarity between the piston and
slide-valve is that they are both employed to control the
admission and release of steam. In all other respects
they are different, but we shall here confine our examina-
tion to the difference in operation between the two.
Operation of the Piston- Valve.
The piston valve is generally of the inside admission
type, with outside exhaust; that is, the inner edge of
the piston valve is the steam edge, while the outer edge
controls the exhaust. As a result of such arrangement
all of the events of the stroke are just the reverse of the
VALVES AND VALVE GEARS
171
slide valve events. This is, as previously explained, be-
cause the slide valve has outside admission, and inside
exhaust, and may be readily understood from the follow-
When the piston valve moves in the direction of the
arrow A, Fig. 54, it will uncover the left-hand port,
Fig. 54.
while a similar movement of a slide valve would mark
the commencement of exhaust, but, with the piston valve
steam is admitted from the inside of the valve at the
point indicated by the arrow a. Admission begins here
and will continue until the valve reaches the end of its
travel to the left, and returns, in the direction of the
arrow B, to cut-off — the position it occupies in the illus-
tration — where the admission of steam to the cylinder
172
MODERN LOCOMOTIVE
ceases, and cut-off takes place at the point &. With the
slide valve compression would now begin. •
Now directing our attention to Fig. 55, we will assume
the valve continues its travel in the direction of the arrow
until the outer edge of the valve coincides with the outer
edge of the steam port indicated by the arrow a. It
Fig. 55.
must be apparent that the steam which has not been ex-
hausted from the right-hand port will be trapped in the
cylinder, and must be compressed by the advancing piston
which is also moving in the direction of the large arrow.
This point, compression, corresponds to the point of cut-
off with the slide valve.
It will be observed that the valve is now in its mid-
position, for the two outer ends of the valve register
with the outer edges of the steam ports; therefore, as
VALVES AND VALVE GEARS 173
the valve continues its movement to the right the ex-
haust of steam will commence, in the left-hand port at b,
whereas the movement of a slide valve in the same di-
rection would allow the admission of steam in the left-
hand port.
From this brief explanation of the difference in opera-
tion between the movements of a piston and a slide valve,
the effects of over-travel, lap, lead, etc., with the piston
valve, must be apparent.
Pistan Valve Cylinders.
Piston valves can be located in almost any position with
regard to the cylinders, and may be made any length
desired. As a result the steam ports of piston valve
cylinders should be made short and direct, and the steam
chest placed close to the cylinder bore, leaving only
sufficient room for the barrel flange to be turned for the
head casting. Piston valve cylinders weigh less than
first class slide-valve cylinders, and are more suitable
to curved lines than the type used with slide-valves.
The Allfree Piston Valve Cylinders.
These cylinders embody firmly established principles
which are applicable to the locomotive, and vary but little
from ordinary practice, common standards being main-
tained. It may be noted, however, by referring to Fig.
174
MODERN LOCOMOTIVE
56, that this type of cylinder is only arranged for inside
admission valves.
The only essential difference in their general construc-
tion and that of other common designs is the use of the
compression valve, and, as this positively actuated valve
eliminates the necessity for, and takes the place of, by-
pass and relief valves, there is no complication or mul-
tiplication of parts.
The Allfree Piston Valve.
This valve requires a special design of cylinder and
steam chest {shown by Fig. 56), so arranged that there
is a cylindrical opening between the main valve and the
piston cylinder, in which an auxiliary compression valve
VALVES AND VALVE GEARS iy$
operates. The main valve is of the ordinary piston type,
communicating with the cylinder through short, straight
ports. The compression valve also is of the piston type.
Fig 57-
smaller than the main valve, and is in communication
with the cylinder. Fig. 57 shows a section through the
main valve and cylinder barrel.
The main valve operates just as the common inside
admission piston valve, opening and closing the ports to
176 MODERN LOCOMOTIVE
the admission of steam, except that it is given about }i
inch exhaust lap. This delays release, and therefore in-
creases expansion. With the ordinary valve this would
not be practical, for if exhaust were delayed too long,
the steam would not all escape from the cylinder, and
excessive back pressure would result. With the AUfree
arrangement, however, the auxiliary valve, although it
has no effect on admission or cut-oft', opens to exhaust
at the point of release of the main valve, and with this
double opening the used steam is easily and rapidly re-
leased from the cylinder.
Delayed release, however, accounts for only a part of
the increased expansion. This valve admits less steam
for a given cut-off than the ordinary valve, because there
is only about one-fourth the usual amount of clearance
between the piston and the cylinder head. It is easily
seen that this reduction of clearance increases the period
of expansion.
With the common valve, when exhaust ends compres-
sion commences, and, with one-third cut-off position,
continues for nearly one-third the entire stroke of the
piston. The compression valve, however, in the AUfree
arrangement, remains open after the main valve closes
to exhaust, and the used steam continues to escape. A
section through the compression valve is shown in
Fig. 58.
VALVES AND VALVE GEARS
177
The compression valve remains open until the piston
has completed all but about two inches of its stroke,
when the valve closes and compression commences. Thin
Fig. 58.
greatly reduced compression adds to the unobstructed
stroke of the piston, reducing negative work in the cyl-
inder. It does not, however, produce a shock on the
piston and its connections, as might be imagined, for the
reduced amount of steam is compressed in a correspond-
178 MODERN LOCOMOTIVE
ingly smaller space, due to reduced clearance, and this
has the same cushioning effect as the greater amount of
steam compressed in the larger clearance space of the
ordinary cylinder.
It is also claimed that a saving in steam results from
the smaller clearance space having to be filled by admis-
sion steam, when the pressure of the compressed steam
does not equal the initial, or boiler, pressure.
This valve was patented July 9, 191 2, by Mr. Edwin
H. Allfree, of Chicago, 111.
m
American Semi-plug Piston Valve.
This is a special form of piston valve, patented No-
vember 17, 1908, by Mr. John T. Wilson, of Jersey
Shore, Pa., which was designed to embody the advan-
tages and to eliminate the disadvantages of the solid
plug type of valve, which becomes leaky with wear,
and the snap ring type, which tends to wear the valve
cage unevenly.
The aim of the designer was to produce a valve which
would automatically obtain a correct contact pressure
between the packing rings and bushing, and then lock
the rings in place, while steam chest pressure continued,
by means of wedge rings under steam pressure.
A detail section of this valve is presented in Fig. 59
and the construction and operation of the valve may be
described as follows :
VALVES AND VALVE GEAfiS 179
The two snap rings numbered "i," are put in under
tension, and are, therefore, self-adjusting; their outside
walls are straight, and fit against the straight walls of
the follower and spool The inner walls of these snap
rings are beveled, forming a cone Next to the snap
rings are wall rings, numbered "2," the outer faces of
which are beveled to fit the cones of the snap rmgs.
\
I II.
Fig. 59.
These are called "wall rings" because they form the
inner walls for the snap rings. These wall rings are
uncut, non-expansible steel rings. Between these wall
rings, in the center, is placed a double coned expansible
ring, called a "wedge ring," numbered "4," the sides of
which are beveled to fit the inner sides of the wall rings.
This wedge ring is put in under tension, and its tendency
to expand crowds the two wall rings laterally against
the cone sides of the snap rings, numbered "i"; this
prevents lateral wear of all rings. A wide ring, num-
l8o MODERN LOCOMOTIVE
bered "3," interlocks with the snap rings, and completes
the packing. The wide ring performs two important
functions: First, it carries the snap rings across ports
while the engine is drifting, and, second, it keeps the
snap rings parallel and of equal diameter, so that the
wide ring and the two snap rings form a flexible, yet
wide, packing ring. The snap rings and the wide, or
separating, ring expand and contract as one ring. All
rings are free to turn around.
The principle of the valve is to control the frictional
contact, or packing, against the cage by a system of
wedges operated by the steam chest pressure, the wedges
being in the form of cones, expansible and non-expans-
ible. Now, having the principle of the valve fixed clearly
in mind, we will note its operation.
The degree of angle on the cones, it will be observed,
is much greater on the double tapered wedge ring than
on the snap rings. These angles are so calculated that,
while the pressure is underneath all the rings, the lev-
erage of the double tapered wedge ring, crowding the
solid wall rings against the cones of the snap rings, is
just sufficient to prevent the snap rings from further
expansion, but not sufficient to reduce the snap rings in
diameter. By a little consideration of the effect of chang-
ing the degree of angle, it will be observed that the
frictional contact of the snap rings against the valve
VALVES AND VALVE GEARS l8l
chamber depends entirely upon the angles, and it may,
therefore, be regulated to any desired degree.
By observing the locking effect of the double tapered
wedge ring, when it is expanded by pressure, thereby
crowding the two solid wall rings laterally, and holding
them, as it were, with a predetermined force against
the cone sides of the snap rings, it will be readily realized
that by sufiiciently increasing the angle of the cones
on the sides of the snap rings and making the solid
wall rings to correspond, the force of the double tapered
wedge ring, crowding the wall rings laterally on a
sharper cone would be sufficient to close up, or decrease
the diameter of the snap rings, regardless of the pressure
under them; under these conditions the leverage would
be too great, and would permit a blow over the outside
of the snap ring. On the other hand, if the degree of
angle on the snap ring were reduced, and the cone made
flatter with wall rings to correspond, then the wedging
power of the central wedge ring would not be sufficient
to prevent the snap rings from being expanded by the
pressure underneath them, and this would result in ex-
cessive friction against the valve chamber, caused by
insufficient leverage to lock the rings. The same effect
may be reached in either direction by changing the de-
gree of angle of the double tapered wedge ring.
1 82 MODERN LOCOMOTIVE
The action of the valve may be summarized as follows :
When steam is admitted to the steam chest, it passes
through the small holes, E, around the spool, and finds an
outlet, first, under the snap ring, and, second, under the
central wedge ring. From 14 to 18 holes are in each
end of the valve. The two snap rings being interlocked
through the wide ring, the velocity of the steam through
these holes against the first snap ring insures the expan-
sion of the packing to fit the valve chamber, and the
velocity acting against the wedge ring places it in posi-
tion for the pressure to lock up the rings. The force
of velocity acts upon these rings before the accumulation
of pressure locks them. While the engine is drifting,
the packing rings contract, due to the lack of steam
pressure, and the engine is thus relieved by allowing
clearance space between the packing rings and the valve
cage.
With this action clearly in the reader's mind, it will
be seen that when the rings are locked in the cage they
will remain of that diameter, unless they are locked in
a large part of a worn cage; for instance, in which the
movement of the valve forces the snap rings into the
diameter of the cage at the smallest part. Under these
conditions the snap rings would remain the smallest
diameter of the cage in which the valve traveled back
to the position of the original locking, and in that posi-
VALVES AND VALVE GEARS 183
tion there would be a blow over the outside diameter
of the snap ring. It will be seen, therefore, that this
valve will never wear a cage out of true, and it will also
be observed that it is very important that the valve be
put into a true cage to begin with, and that the bushing
must be kept true, to obtain satisfactory service.
The valve cage, or liner,, is shown in Fig. 60, as is
the extension valve stem and bearing. This extension
Fia 60.
valve stem is essential to the use of this valve, as the
valve must be carried central, or nearly so, and the
spool must not be permitted to ride on the cage, or bush-
ing, as this causes wear and a leaky valve. Although
the arrangement is rather complicated, it has generally
given satisfactory and efficient service in actual prac-
tice.
This valve is well balanced, and gives good service
while new, but it is expensive to repair when worn. In
some cases trouble was experienced with broken rings,
due to the fact that the rings had worn to the breaking
184 MODERN LOCOMOTIVE
point without renewal. The manufacturers now over-
come this trouble by applying dowel pins to the connect-
ing slot on the sides of the steam and exhau3t rings, so
that the valve will give warning by blowing before the
rings have worn to the breaking point.
The Young Piston Valve.
This valve consists of a light spool-shaped cylinder,
cast in one piece, the ends of which are of hollow con-
struction, resembling somewhat the bushings applied to
the ordinary piston valve chamber. These hollow ends
are each made with two rows of openings, or ports, as
shown in Fig. 61. The distance between the two rows
of port holes in each end is so fixed that the valve alter-
nately admits steam into the cylinder and allows it to
escape, through the ports, in the same manner as the
common inside admission piston valve.
The packing rings, instead of being placed in the
valve to expand against the bushing, are fitted in suit-
able grooves in the valve chamber, on either side of
each cylinder port, the outer surfaces of the valve ends
being in sliding contact with them. The rings are of the
split compression type, designed to contract against the
cylindrical surface of the valve, and are spaced, by
filling blocks, to their desired diameters.
This arrangement provides a valve which, after very
slight wear to take up the original clearance between
VALVES AND VALVE GEAB5 185
the divided ends of the rings and their filling blocks,
is practically steam tight. The operation of the valve
is very similar to that of the ordinary solid plug form.
However, due to its construction, the Young valve elim-
inates the many disadvantages of the plug type, more
especially that of excessive weight. In fact, this valve
is unusually light, for a twelve-inch valve will weigh
but one hundred pounds, or about half- the weight of
Fig. 61.
the common piston valve of the same diameter. This,
of course, means a reduction in friction, and less stress
upon the valve gear.
The valve is made with a special valve stem, which is
provided with a knuckle. This knuckle is secured to
the center of the valve spool by a fitted pin, and it is
thus possible for the valve to align itself regardless of
the alignment of the stem, eliminating uneven wear on
the valve and the packing rings. This valve is shown
in its position in the cylinder in Fig. 112.
l86 MODERN LOCOMOTIVE
This valve was invented by Mr. Otis W. Young, of
Qiicago, 111., and is manufactured by the Pyle-National
Company, of Chicago, 111.
Piston versus Balanced Slide Valye.
As previously stated, the balanced slide valve was
employed in locomotive service for several years before
the piston valve was adopted, and the latter type was,
by many, looked upon with disfavor. As a result each
type of valve has its champions and there seems to be no
unanimity of opinion regarding the merits or demerits
of either type of valve.
The writer is not prompted by personal interest in ad-
vocating the advantages or disadvantages of either valve,
so we therefore present an impartial review of what
may be considered the weight of opinion regarding each
type of valve at the present time.
Advantages af the Piston Valve.
The principal advantage of the piston valve over the
balanced slide valve is the fact that it is more fully
balanced, and therefore more easily manipulated from the
cab. As a matter of fact, piston valves are generally
handled with greater ease when the throttle is open
than when it is closed, which is just the reverse of slide
valves. The larger piston valves are almost as easily
manipulated as the smaller ones.
VALVES AND VALVE GEARS 187
The piston valve is probably more economical in steam
consumption than the slide valve, but much depends upon
the design and maintenance of the valve in question.
If piston valves were given as much attention in the
roundhouse as slide valves, they would, no doubt, show
less steam loss from valve leakage than the balanced
slide valve type.
Because they can be placed in almost any position with
regard to the cylinder, the piston valves give flexibility
of design. These valves can be placed above the cylinder,
between the frame rails, or in nearly any position, thus
they are adaptable to any form of valve gear. Piston
valves can be made of any desirable length; therefore
the steam ports can be made very short and direct.
With inside admission valves (piston valves are nearly
always of this type; slide valves are not) the steam
chest heads and packing are relieved of all pressure ex-
cept that of exhaust steam, which puts very little stress
upon these parts.
The cylinder casting used in connection with the piston
valve is lighter and cheaper than that required for the
slide valve, and the wearing surface, or bushing, is sep-
arate from the casting and can be renewed at a slight
cost. The piston valve excels the slide valve in regard
to maintenance cost.
l88 MODERN LOCOMOTIVE
The better balance of the piston valves, together with
the reduced frictional resistance, relieve much wear and
tear on the valve gear operating it, especially when super-
heat is used.
Disadvantages of the Piston Valve.
The piston valve has one decided disadvantage ; it can-
not relieve excessive pressure, or water in the cylinder.
Many forms of relief valves have been used to accomplish
this result, but they are expensive to maintain, and none
give satisfactory results.
In some cases it has been found difficult to lubricate
piston valves, more especially while drifting. Other de-
fects are cut and broken packing rings, edge of spool
breaking, liability to blow, excessive wear on bushing
at short stroke, and friction due to the pressure of steam
under the packing rings. The broken packing ring is
not a serious trouble unless it catches in the port; the
result IS then a broken or sprung valve gear. Some
roads report that, with piston valves, the main driving
boxes wear so rapidly as to create side play and pound.
Advantages of the Slide Valve.
The chief advantage of the slide valve lies in the fact
that it can relieve excessive pressure in the cylinder and
steam chest by temporarily lifting from its seat. This
VALVES AND VALVE GEARS 1 89
eliminates the troublesome relief valves used for this pur-
pose with piston valves.
The balanced slide valve, which is practically the only
kind now in use, tends to eliminate the excessive friction
of the ordinary D slide valve. This is accomplished, as
previously described, by the use of balance strips, and
pressure plates, above the valve. This is really not an
advantage of the slide over the piston valve, but rather
an advantage which the balanced valve has over the plain
D slide valve.
A few roads employ special methods of lubrication,
and obtain satisfactory service from the use of balanced
slide valves with superheat, but it it admitted that this
service is excelled by the use of the piston valve.
Disadvantages of the Slide Valve.
When moving on its seat, even a well balanced slide
valve creates excessive friction. This is especially true
with the use of large cylinder dimensions and high steam
pressures common to modern locomotives. This friction
causes rapid wear on the valve, valve seat and gear, and
it is very uncommon for an engine with slide valves to
run 25,000 miles before the valves require facing. The
large steam chests necessary also cause condensation of
steam, which accounts for the high water rate of engines
so equipped.
190 MODERN LOCOMOTIVE
There is sometimes an upward pressure on the face
of the slide valve, which causes a rocking motion, thus
wearing the corners of the valve. When these comers
are rounded, the valve is not tight, but will leak steam.
Ordinarily, slide valves cannot be operated successfully
with superheat because of the high steam pressure. Thus,
with the advent of the large and more modem locomo-
tives, the balanced slide valve is fast giving way to the
more efficient piston valve.
The cost of maintenance of the slide valve exceeds that
of the piston type. The balance feature must be retained
in good condition, and this necessitates much care. False
valve seats are often necessary, when the valve seat wears
to the limit. These are expensive to machine and apply,
and are not altogether satisfactory.
Because the slide valve chest is subject to boiler pres-
sure, it is no light task to prevent steam leaks in the
joints at the top and bottom of the steam chest. The
valve stem must be packed against boiler pressure,
whereas the stem of the piston valve, is subject merely
to exhaust pressure. If steam leaks, lubrication is to a
certain extent destroyed.
The pressure plate of the slide valve is often cut by
the end balance strips. Many roads weaken the springs
under these strips, or reduce their number, to overcome
this difficulty.
VALVES AND VALVE GEARS IQI
The slide valve requires much more space than the
piston valve, and adds greatly to the weight of the cylin-.
der casting.
The most common failures experienced with the use
of the slide valve are broken valve yokes and stems, due
usually to cut valve seats, faulty lubrication, or defects
in the balance feature of the valve.
Universal Valve Chest.
An ingenious arrangement for the application of piston
valves to cylinders primarily designed for slide valves,
was invented July 14, 1914, by Mr. John E. Muhlfeld,
of Scarsdale, N. Y., and Mr. Hal R. Stafford, of Plain-
field, N. J.
We understand that the device has been successfully
adapted to every design of slide valve cylinder in service.
In fact, it can be designed for every combination, for the
application of the device permits the use of superheated
steam with the old cylinder, at almost the same cost as
cylinders originally designed for -piston valves, with the
same effect and power, for either inside or outside ad-
mission valves, and may be used with any type of valve
gear in use at present.
There are two distinct types of this valve chest, viz.:
In type A, Fig. 62, a separate inner valve chamber is
jointed to the valve seat, independent of the outer chest,
192
MODERN LOCOMOTIVE
which is seated on the cylinder apron in the usual way.
Thus the regular inlet ports to the steam chest may fae ■
utilized. This type is also designed for use with either
inside or outside steam pipes.
On the other hand, type B, Fig. 63, is designed for
use where new outside steam pipes are to be applied.
Fig. 62.
This type is made in one piece, is joined to the valve
seat only, and by a system of joint wires set in grooves,
around the chest and each separate port, is rendered steam
tight.
An end view, in cross-section, of both valves is shown
in Fig. 64. On the left is shown the type B, Fig. 63,
which calls for the application of new outdde steam
pipes. On the right, type A, Fig. 62, designed for use
VALVES AND VALVE GEARS
193
[ with either iiiside or outside steam pipes, is represented.
[ This combination of the two figures ciearly illustrates
f the difference in construction of the valve chest to be
[ used with either type.
: feature claimed for the invention is that it
I
Fig. 63.
permits the use of a valve of muiimum diameter, because I
the steam ports are of such form that the entire circum- |
ference of the valve is effective.
The advantages gained by the use of the small valves
will be readily appreciated by practical mechanics, for
the decrease in size reduces friction and stresses pro-
portionally, and results in a better steam distribution.
194 MODERN LOCOMOTIVE
The Economy Device Corporation, of New York City,
are the manufacturers of this device.
Fig, 64,
A Straightway Piston Valve Arnuigement.
A new method, or arrangement, of restricting the size
of the valve for ordinary piston valve cylinders, in ac-
cordance with the established principles of the flow of
g;ases, without sacrificing the amount of work generally
secured by the use of a larger valve, is described and
illustrated herewith.
VALVES AND VALVE GEARS
195
With the use of this device it is unnecessary to make
the circumference of a piston any greater than the
len^h of a slide valve port, for the beneficial effect is
obtained by properly directing the flow of steam to and
from the valve so that every square inch of the bushing
Fig. 65.
port will become effective. This permits the use of a
valve only half the size commonly used, and, at the same
time, facilitates the flow of steam to and from the cyl-
inder to such an extent that the engine is much smarter
and faster.
Fig. 65 shows the application of these principles to
new power, where the design of the cylinders is under
196 MODERN LOCOMOTIVE
control. The letter Y equals the area of each bushing:
port, while X equals Y in area. Thus it will be seen
that the steam port around the bushing is so arranged
that, during the admission period, as steam issues from
the valve, it is divided into a number of streams, de-
Fig. 66.
pending upon the necessary number of bridges in the
bushing. These streams are directed by the ribs so
that they do not interfere with each other, but join into
one smooth flowing whole when the main passage is
reached. During the exhaust stroke the steam, as it
flows from the cylinder to the valve, is divided by the
ribs into a number of equal streams, one from each port
in the bushing.
VALVES AND VALVE GEARS lofj
This absence of all quick turns, or other obstructions,
speeds up the flow of steam, and, with an eight or ten
inch valve, gives a higher initial pressure and a better
admission line than can be obtained with the ordinary
design of port with a fourteen or sixteen inch valve.
Fig. 66 shows the method of applying small valves to
existing engines on which valves of much larger diam-
eter were originally used. In this case a new bushing
of special design, in which the directing ribs are cast
as a part of the bushing bridges, is applied in place of
the original bushing. This arrangement makes it pos-
sible to secure the advantages of the smaller and lighter
valve, and gives a steam distribution at least equal, and
in most cases superior, to that of the larger valve.
This device is also manufactured by the Economy
Devices Corporation, of New York City, N. Y.
Sheedy's Outside-steam-pipe for Piston-valves.
This device was invented by Mr. Patrick Sheedy, of
Los Angeles, Cal., and a patent was issued to him on
September 5, 1916.
The object of this invention is to effect a material and
substantial economy in the modernization of existing
locomotives which relates to improvements in cylinder
construction, by a simple and inexpensive method of
converting existing cylinders in which steam is supplied
through an inside steam pipe, to a steam passage in the
MODERN LOCOMOTIVE
cylinder saddle, into cylinders, adapted to be supplied
with steam through an outside steam pipe.
The advantages o( effecting steam supply to locomo-
tive cylinders through what are known as outside steam
Fig. 67.
pipes, particularly in facilitating draft by relieving the .
lower portion of the smoke box from obstruction, elim-
inating steam leaks through the bottom steam pipe joints
in the smoke box, and promoting the application of
superheaters, are so well and thoroughly recognized, that
VALVES AND VALVE GEARS 199
in practically all new locomotives the cylinders are pro-
vided with outside steam pipes.
When it has been considered necessary to modernize
existing locomotives, by the application of recent im-
provements in structural detail, the inside steam pipe
cylinders have been scrapped and new cylinders with
outside steam pipes substituted, but such a change can
only be made at considerable cost.
This invention provides a method of applying outside
steam pipe cylinders of the latest pattern to old style
locomotives with inside steam pipe connections, without
a change of the original cylinder at considerable saving.
Fig. 67 shows a section of a cylinder, commonly used
in locomotive construction, and Fig. 68 another view
of the same cylinder equipped with the device under
consideration. First a rectangular transverse passage-
way is cut in the top of the valve chest, symmetrically
with the middle transverse plane thereof, and an inte-
gral bushing, termed a finger ring bushing, is then
dropped through this opening into the valve chest, and
secured therein with its horizontal bore in line axially
with the valve bushings. The bushing is open at the bot-
tom on its opposite sides to the valve bushings, and is
open at top which is adapted for connection to the lower
end of an outside steam pipe, a ball joint ring being inter-
posed between it and the steam pipe. The bushing is
MODERN LOCOMOTIVE
connected to the valve chest bj' bolts passing through
a circumferential flange on Ihe bushing the under side
of which is curved in conformity with the adjoining
outer surface of the valve chest. The bushing is then
Fig. 68.
bored out in line axially with valve bushings, and valve
bushings are pressed steam tight into opposite ends of
the valve chamber in which they are permanently located.
The original steam passage may then be filled with a
mixture of cement and iron borings to support the bush-
ing and prevent deterioration due to the entry of mois-
ture into the unused passage.
VALVES AND VALVE GEARS 201
It wil! be seen by the above method of reconstruction,
which can be effected at comparatively slight expense,
an outside steam pipe may be applied to a locomotive
cylinder, which was originally designed for inside steam '
pipe supply with the same facility as if the latter had
been as constructed, adapted for such application, and in
the improvement or modernization of the locomotive, in
this particular, the very substantial economy of avoiding
the abandonment and scrapping of a very valuable pair
of cylinders.
202 MODERN LOCOMOTIVE
VALVE GEARS.
Introductian.
The necessity of a device for reversing, or changing,
the motion of a locomotive was promptly recognized in
the early days of locomotive construction, and numer-
ous devices, which are known as "valve gears," have
been invented to accomplish the result desired.
The first, or original, device employed to reverse a
locomotive consisted of a single eccentric which was
loose on the shaft, and could be turned by a hand wheel.
When the steam was shut off and the engine brought
to a stop, the engineer could go forward and loosen
a nut, turn the eccentric around to the position desired,
screw the nut tight to clamp the eccentric in its new
position, and proceed in the opposite direction.
We assume the original device did not give entire
satisfaction, however, and it may not have been popular
with the engineers of that day, for another reversing
valve gear, called the •"gab-hooks,'* Fig. 69, was de-
vised which employed two eccentrics and enabled the
engineer to change the motion of the engine without
leaving the cab. Each eccentric-rod had a notched hook
attached to its forward end, and the back end of the
valve-rod carried a pin on which the notched hooks
VALVES AND VALVE GEARS
203
could be brought into contact to actuate the valve. When
the upper hook was lowered to connect with the valve-
rod pin the forward eccentric operated the valve, and
vice versa.
The result of lowering or raising a hook to catch
a pin in the end of the valve-rod to reverse the move-
FiG. 69.
ment of a high speed locomotive of the present day can
be better imagined than described.
The only noteworthy thing about this form of valve
gear is that it was the first, and the last, to use hooks,
and it introduced the principle, which has been adopted
by numerous inventors since, of using two eccentrics.
The next step toward the improvement of valve gears
was the introduction of the curved or straight link which
204 MODERN LOCOMOTIVE
IS at present employed in connection with practically
all reversing valve gears. This was, in fact, a great
improvement, not only in providing for the reversal
of the locomotive, but because it provided means of al-
lowing a variation in the arrangement of the valve
mechanism, thereby permitting a more economical steam
distribution in the cylinder.
Numerous other valve gears appeared from time to
time, but they did not possess sufficient merit to sup-
plant the Stephenson link-motion which was, for many
years, used exclusively in American locomotive construc-
tion.
With the introduction of the powerful locomotives
of the present day, however, it was found the Stephen-
son link-motion could no longer be used to advantage
and, for structural reasons, it was replaced by the vari-
ous types of outside valve gear, which will be described
later on. We do not believe, therefore, that a descrip-
tion of it would be of advantage to the reader, so we
shall confine our discussion to the modern valve gears
in use today.
We deem it proper to first describe the pioneer radial
valve gear which is most extensively used, and whose
popularity has steadily increased since its adoption in
American locomotive construction — the Walschaert.
VALVES AND VALVE GEARS 20S
THE WALSCHAERT VALVE GEAR.
HISTORY.
Before proceeding into a discussion of this well known
form of valve gear, it seems to the writer that a brief
history of the life and work of the inventor should be
of interest to the reader, and with this idea in mind
we present the following facts :
The inventor of this valve gear was born in Malines,
Belgium, on January 21, 1820, and was named Egide
Walschaerts. Some vears later, for reasons unknown
to the writer, he saw fit to omit the final letter s from
his surname, so we shall do likewise in referring to
him in this work.
About the year 1835, when the line from Brussels
to Malines was opened, his native city was made the
central point of the Belgium State Railways. The event
proved to be the turning point in the career of young
Walschaert, for the construction of the locomotive made
a strong impression on his mind, which lasted until
the end of his life.
In 1838, while a student in the College of Malines,
he exhibited some models of a stationary and a locomo-
tive engine of his own construction, at a local exposi-
tion. He continued his experiments with more or less
success and secured a position as a mechanic in the
206 MODERN LOCOMOTIVE
Belgium State Railway shops in Malines in 1842, and
became a foreman in the shops at Brussels Uyo years
later, when his ability as an engineer had clearly dem-
onstrated his qualification to rule the motive depart-
ment, yet he was never permitted to rise to a higher
official position.
In those early days the locomotives used in Belgium
were imported from England, and they had only been
in service a few years when Walschaert was made a
foreman. But it is now evident that they did not meet
with his approval, for he soon began work upon a new
system of valve motion, which invention he completed
in the year of 1844.
Under the rules of the Belgium State Railways, in
force at that time, a mechanic, or foreman, was not al-
lowed to patent a discovery or device for his own bene-
fit and profit, because the product of his brain, as well
as his hands, was considered the property of his em-
ployer. So to circumvent the rule Walschaert induced
an engineer of the Belgium State Railways to seek a
patent for him. The application for this Belgium patent
was filed by his friend, Mr. Fisher, on October 5, 1844,
and the patent was issued November 30, 1844, for a
term of 15 years.
It may be stated here, to the credit of Mr. Fisher, that
he never claimed credit, personal or otherwise, for the
VALVES AND VALVE GEARS
208 MODERN LOCOMOTIVE
invention of the valve gear on which he secured a pat-
ent.
The rule referred to, however, did not apply to for-
eign countries, and Walschaert secured a patent on his
valve gear in France on October 25, 1844, in his own
name.
The invention immediatelv attracted attention in Bel-
gium, but some time elapsed before it was adopted by
the leading railways of Europe. Considerable effort
was made to introduce the valve gear in America about
10 to 15 years after it was invented, but the construc-
tion of our locomotives and the existing conditions were
not then favorable. About 1897 a few American loco-
motives were equipped with the gear and the results ob-"
tained during the following years were so satisfactory
that the valve gear gradually worked its way into gen-
eral favpr.
The original design of Walschaert's valve gear, upon
which a Belgium patent was issued to his friend Fisher,
is shown in Fig. 70.
While there is considerable difference in construc-
tion of the mechanism patented in 1844, it is, in prin-
ciple, similar to the valve gear in use today, which was
constructed by Walschaert in 1848, and first used on
locomotive No. 98 of the Belgium State Railways, when
it ran from Malines to Brussels on September 2, 1848.
VALVES AND VALVE GEARS
While it is true the link and
• combination lever are now us-
ually placed in a different posi-
tion to shorten the eccentric and
valve stem, Fig. 71 of the orig-
inal design shows, in a general
way, the valve motion in use to-
day, for quite a number of loco-
motives at the present time re-
quire an arrangement similar to
that of the illustration.
At the time Walschaert began
his work, Sharp's valve-motion, 3
which consisted of two eccentrics ^
with forked rods, was the only. *
system in extensive use, and it
is very doubtful whether Wals-
chaert ever saw the link motion
credited to Stephenson, which
was in fact invented by Howe in
1843, before he completed his
own system.
The inventor's activity during
the following years was confined,
to a great extent, to the duties
imposed on him as foreman, but
I
2IO MODERN LOCOMOTIVE
a number of other improvements and inventions con-
ceived in his ingenious brain were used by practical men
^ of that time.
M It is now difficuJit Jb understand how Walschaert's
inventive spirit wIP nraintained in the face of the ob-
stacles encountered, and the field to which his services
were restricted. It certainly was not stimulated by any
monetary reward, for he never received much, if any-
thing, except a few medals, for the invention of his
valve gear. .»
Then death deprived him of the pleasure of seeing
the general adoption of his valve gear by the locomo-
W^ tives of the .twentieth century, for he died on February
i8, 1901, at Saint Gilles, near Brussels, in Belgium, at
the age of 01 years and 29 days.
It has been well said that his work now meets re-
quirements which did not exist during his lifetime and,
for this reason," "hf J is entitled to credit for solving a
problem of, ^;&ftjr^ a future generation.
J Analysis.
I The principal advantage of this gear lies in the ac-
cessibility of its paii^s, which are placed entirely out-
! side of the driving wheels; this facilitates oiling, in-
, specting anfd cleaning operations which are frequently
' difficult »-SiP' performing on locomotives equipped with
the Stephenson link motion. Furthermore, in heavy en-
. ■■■•-tit-": •
VALVES AND VALVE GEARS * ^H
gines equipped with the Stephenson gear, the eccentrics
must be made of large diameter to secure the required
throw. This increases the velocity of the rubbing sur-
faces and tendency to heat, especially in the case of loco-
motives which have comparatively small wheels and are
employed in high speed service.
In the Walschaert gear the various parts are pin-
connected and are easily lubricated, hence troubles due
to heating are reduced to a minimum. Furthermore,
the Walschaert gear, as usually constructed, transmits
the moving force of the valve in a practically straight
line; consequently there is less springing and yielding
of the parts than in the Stephenson link motion.
By removing the valve gear from between the frames,
as in the case of the Walschaert valve gear, a better
opportunity is afforded to introduce stronger frame brac-
ing, and this reduces the possibility of the frame break-
ing. It is purposed here to explain the theory and ac-
tion of the Walschaert valve gear, in as simple and plain
a manner as possible, with the help of numerous illus-
trations.
In commencing the study, or entering into an analy-
sis, of any particular form of locomotive valve gear, it
must be assumed that the principle of the plain steam
engine in its most primitive form is already understood,
at least, of the valve itself. As to the valve, it is a study in
jT
212 MODERN LOCOMOTIVE
itself, and we must become acquainted with it before
starting into the subject of the mechanism that operates
'it.
So far as the distribution of steam in the cylinder is
concerned, the constant lead, which is a feature of this
motion, is not considered objectionable, and it has some
distinct advantages. Under such conditions it is pos-
sible to determine the amount of lead the engine should
have at the most economical point of cut-ofB. This
point once determined, and so designed, it cannot be
altered by anyone in the shop or roundhouse. Another
advantage is that it prevents valve setters from attempt-
ing to produce results by moving the eccentrics into im-
proper relations one to another.
The constant lead of the Walschaert valve motion pre-
vents the sealing of the cylinders by the piston valve
when the piston is at the end of its travel, or approach-
ing it, whereas with the link motion, either by derange-
ment or excessive wear, the valve laps the ports at the
end of the stroke, thereby causing excessive compression
and many other troubles.
Another feature of this motion, which appeals to the
engineers, is the ease of handling the reverse lever when
the locomotive*- is running at a high rate of speed.
Lead is given in order that steam may be admitted
between the piston and the cylinder head, toward the
VALVES AND VALVE GEARS 21 ^
completion of the stroke, as a means of cushioning the
piston and thus tempering the sudden reversion of its
motion. There are many cases in which the variable
lead is preferred; for instance, with a variable lead, the
longest cut-off in starting can be obtained, combined
with the proper amount of lead at the ordinary running
cut-off.
Iti the case of passenger locomotives particularly, a
steam distribution like this is often desirable. The
Walschaert valve gear, as already stated, may be de-
signed to give a variable lead. This practice has recently
been followed in a number of instances. The favor-
able results for starting are, however, obtained at the
expense of the distortion of the valve events in back
motion by robbing one to favor the other.
For this reason the Walschaert valve gear, with
variable lead, is suitable only for passenger and fast
freight locomotives and not for slow freight or switch-
ing locomotives. With a variable lead, so arranged
that the lead increases as the reverse lever is hooked up,
the eccentric crank lags behind the correct position
for a constant lead; in other words, it is so set that
the link is not in its central position when the crank
pin is on the center. The general arrangement of the
Walschaert valve gear depends largely on the gen-
eral design of the locomotive.
214 MODERN LOCOMOTIVE
OoiDstraction.
The reliability of the Walschaert valve motion on
locomotives, when properly applied, has practically put
the former standard (the Stephenson motion) out of
use. It is, therefore, considered that a complete ele-
mentary explanation of the theory of this gear, as
applied in practice* is desirable.
This will involve considerable repetition of data which
has been previously published, but the object is to show
more intimatelv the fundamental co-relation between
the various parts that make up this gear, in order to
UKike as plain as possible its extreme simplicity and to
enable even a laxinan to master the gear without further
instruction.
Like anv other device, the Walschaert valve snotion
is merely ;\ development of some more simple fc»nn. A
clear understanding of the underh*ing principles of this
valve gear is, therefore, best obtained by starting with
the original fonu and tracing the various steps in the
ilovelopment,
iMg. ;*J represents a simple form of vahre motkxi.
This ovMisists of a single crank eccentric, driving a
plain valve without lap or lead, by means of an eccentric
nvl vHrectly vvnnecrev: to the valve stem. Assume that
the eixgine is to run forward; with the main pin on
the back cxnxter, as shvnvn. the eccentric crank pin most
VALVES AND VALVE GEARS
be on the top quarter. The valve
will then be in a central position
on its seat with all ports closed.
The engine could not, therefore,
start of itself when the throttle
was opened. Connect another en-
gine of the same kind to the wheel
on the other side of the axle.
If, then, the main pins are set at
right angles to each other, as in
the case of the locomotive, the
valve of the left hand engine
would be in a position to admit ^
steam behind its piston and start vj
the engine forward. The eccen- '
trie crank of the engine shown in
the illustration would then move
its valve forward. This would
uncover the back steam port and
admit steam behind the piston.
Such an engine, however, would
run in only one direction. If, for
example, the wheel was pinched
backward to start the engine back-
ward: with the eccentric crank in
the position shown, the valve
2l6
MODERN LOCOMOTIVE
would be moved back. Steam would be admitted ahead
of instead of behind the piston.
In order to make the engine run backward, the eccen-
tric would have to be on the lower quarter. In such
a case, if the wheel was turned to the left or back-
ward, the eccentric would be a quarter of a revolution
ahead of the main pin. It would thus move the valve
forward, opening up the back port and admitting steam
behind the piston.
The introduction of some means for reversing is the
first step necessary in the development of this simple
form of engine. This can be accomplished by intro-
ducing between the eccentric crank* and the valve stem
a beam pivoted at its center as shown in Fig. 73. Here
the link is the beam.
Referring to diagram *'A," Fig. 73, with the valve
stem connected to the lower end of the link and the
main pin on the upper quarter, the valve is in the posi-
tion to start the engine forward. Assume, on the other
hand, that the main pin and eccentric crank remain in
the same positions and the valve stem is connected to the
upper end of the link, as shown in diagram "B." The
valve is then in its extreme position to the left. When
the throttle is opened, the engine will run backward.
It is evident, then, that a radius rod connected to a
block which slides in a curved slot in the link, as shown
^
VALVES AND VALVE GEARS 217
2l8 MODERN LOCOMOTIVE
in the diagram, and the necessary mechanism for rais-
ing and lowering the block, would give an engine which
could be reversed.
This engine, however, is far from an efficient ma-
chine. The valve does not close the admission port until
the main pin is on the center, at which time the valve
is in its central position on the seat. Steam will thus
be admitted to the cylinders throughout the full stroke
of the piston, irrespective of the travel of the valve.
In order to govern the period for the admission of
steam; or, in other words, to change the cut-off; a dif-
ferent design of valve must be used. The valve must
be given lap. Also, the valve should have lead, at least
at the ordinary running cut-off.
If lap and lead are given to the valve, the valve mo-
tion shown in Fig. 73 must be so modified that, when the
crank pin is on either of the centers, the valve will be
advanced a distance equal to the lap plus the lead.
A study of Fig. 74 shows that this advance of the
valve cannot be obtained by any change in the position
of the eccentric crank relative to the main pin. With
a single eccentic crank, as shown, the engine could not
be reversed if the eccentric crank was not a quarter
of a revolution from the main pin.
Fig. 74 shows the same valve motion as Fig. 73; ex-
cept that the valve has one inch outside lap and the
VALVES AND VALVE GEARS 219
1
1
i
220 MODERN LOCOMOTIVE
eccentric crank has been advanced to more than a quar-
ter of a revolution ahead of the main pin. With the
link block at the bottom of the* link, as in diagram
"A," the advance given to the eccentric will have moved
the valve forward a distance equal to the lap plus the
lead, and the engine will run forward. But if the link
block were moved to the upper end of the link, as in
diagram "B," the valve would be moved back. Steam
would then be admitted to the front end of the cylinder
when the piston is at the. end of the back stroke. The
engine would then stall and, therefore, could not be
reversed.
In the Walschaert valve gear, the motion for pro-
viding lap and lead to the valve is derived from the
main pin through the lap and lead lever, which is con-
nected to the crosshead.
The introduction of the lap and lead lever is the
next step in the development of the Walschaert valve
gear.
Referring to Fig. 75, when the link block is in the
center of the link, as in diagram "A," there will be no
movement of the radius rod as the link is swung back
and forth by the eccentric. Assume that the radius rod
is connected with the lap and lead lever at the point
"R." Also assume that the upper end of the lever is
connected with the valve stem crosshead at "V/* and
VALVES AND VALVE GEARS
222 MODERK LOCOMOTIVE
the lower end to the crosshead arm by a short link, as
shown. With such a construction, as the crosshead
moves hack and forth, point "R" being stationary, the
point "V" will rotate about it. The valve will thus be
moved back and forth.
With the inain pin on the forward center, as in dia-
gram "A," the angle assumed by the lap and lead lever
has moved the valve back a sufficient distance to un-
cover the front port. When the main pin is on the back
center, as in diagram "B," the inclination of this lever
has opened the back port.
Therefore, the motion of the valve is derived froi
two distinct sources, viz. : the eccentric crank and th(
main crank. The former gives the travel to the val'
minus the lap and lead. This motion is transmitte<
through a slotted link oscillating on a fulcrum, in whi
slot the link block is moved at- will above or below the
fulcrum. By this means the motion of the engine can
be reversed so as to run either forward or backward
and it may, therefore, be called the reversing motion
of the gear. The lap and lead motion, imparted to the
valve by the main crank, is not reversible, as it is
symmetrical with relation to the dead center position
of the crank in whichever direction the engine is run-
ning, land is always constant, regardless of the position
of the link block.
ich^fl
VALVES AND VALVE GEARS
MODERN LOCOMOTIVE
VALVES AND VALVE GEARS
225
MODERN LOCOMOTIVE
VALVES AND VALVE GEARS ^2^
The action of the VValschaert valve gear as a whole
may be best learned by tracing the movement of the
valve through a complete revolution of the wheel.
Figs. 76 to 79 show a series of diagrams representing
different positions of the crank pin. For the sake of
simplicity, the valve and cylinder are shown in section.
The other parts of the gear are represented by their
center lines and center points only. These diagrams
are purposely drawn out of proportion. The valve and
the eccentric throw have been enlarged in order to
show more clearly the positions of the edges of the
valve relative to the edges of the cylinder ports.
In Fig. 76 the valve has outside admission; and the
motion is represented with the reverse lever in full
gear forward. Fig. y] represents the same arrangement
of valve motion. In this latter case, however, the re-
verse lever is hooked up and the engine is cutting off
at about 25 per cent of the stroke.
Figs. 78 and 79 represent the Walschaert valve gear
as arranged for piston valves having inside admission.
In the Walschaert valve gear, the valve, as previ-
ously explained, receives motion from two distinct
sources: First, from the eccentric crank. This gives
the valve its full travel. Second, from the lap and lead
lever. This gives the valve its lead. The valve would
receive a travel from this source equal to twice the lap
228 MODERN LOCOMOTIVE
plus twice the lead, even if the eccentric rod was dis-
connected.
Considering diagram i, Fig. 76, the valve has out-
side admission. Consequently, forward motion being
taken from the bottom of the link, the eccentric crank
leads the main pin. Also the radius rod is connected
to the lap and lead lever below the valve stem.
The link is in its central position. Therefore, the
valve would likewise be in its central position, if it
were not for the motion given to it by the lap and lead
lever. The travel of the crosshead to the back end
of the stroke has caused this lever to rotate about its
point of connection with the radius rod'. This has
moved the valve forward, as indicated by the arrow, a
distance equal to the lap of the valve plus the lead.
Considering diagram "i," Fig. ^T\ the main pin, ec-
centric crank, link and crosshead are in the same posi-
tions as they are in the corresponding diagram in Fig.
76. The link block, however, is nearer the center of the
link. This has not affected the lead for the following
reasons: The length of the radius rod is the same as
the radius of the link, or approximately so. Thus, as
the link is in its central position the raising of the link
does not cause, any movement of the front end of the
radius bar. This point, which is the fulcrum of the
lap and lead lever, is in the same position as in the
VALVES AND. VALVfe GBARS 22g
diagram previously considered. Consequently, this lever
has moved the valve to the same position as before;
and the lead is the same as when the reverse lever was
in full gear.
In Figs. 78 and 79 the valves have inside admission.
The radius rod is thus connected to the lap and lead
lever above the valve stem.
The diagrams in Figs. 76 to 79 represent the various
valve events throughout a complete revolution of wheels.
Comparison between corresponding diagrams in the
four figures brings out very clearly the difference in
the arrangement of the Walschaert valve gear for out-
side and inside admission valves. It also shows the
effect on the various valve events of hooking up the
reverse lever. For example, it will be noticed that in
Figs, yy and 79 the valve cuts off the steam from the
cylinders and opens the steam ports to the exhaust
at a much earlier period in the stroke than it does in
Figs. 76 and 78. The latter figures represent the engine
with the reverse lever in the corner notch; while Figs.
yy and 79 represent running with a short cut-off.
With the eccentric crank a quarter of a revolution
from the main pin, and with the eccentric of such
length that the link is in its central position at th> end
of the stroke, the lead in the Walschaert valve gear is
the same for all cut-offs.
230 MODERN LOCOMOTIVE
To change the lead of the Walschaert valve gear,
under the conditions given in the preceding paragraph,
it is necessary to change either the lap of the valve
or the distance between the connecting points of the
lap and lead lever. Reducing the lap of the valve in-
creases the lead, and vice versa. Qianging the lap
also changes the points of cut-off. If the lap is re-
duced, the cut-off will occur at a later period in the
stroke; while if it is increased the opposite result will
occur.
The following rules govern the changes to be made
in the lengths of the arms of the lap and lead lever to
increase or decrease the lead:
To increase the lead, make the upper arm (or
distance between the valve stem and radius bar con-
nections) longer in proportion to the lower arm (or
distance between the radius rod connection and bottom
connection of the lever).
To decrease the lead, make the upper arm shorter in
proportion to the lower arm of the lever.
Arrangement.
A general outline of the gear for an inside-admission
valve is shown in Fig. 80, where the names are given of
all essential parts.
VALVES AND VALVE GEARS
232 MODERN LOCOMOTIVE
The names define, as nearly as practicable, the spe-
cial function each one has to perform in the combi-
nation of the gear. Starting at the crank pin "D" we
have the eccentric crank, eccentric rod, link, radius rod,
combination lever, combination link, crosshead arm and
link block "g" (indicated only by letter). Fig. 81 is
a similar arrangement of an outside-admission gear with
no change in the names of any of the working parts.
It will be noted that in Fig. 80 the eccentric crank
follows the main crank, while in Fig. 81 it leads. Also
in Figs. 80 and 81 the radius bar is shown in the bottom
portion of the link in forward motion, thereby reducing
the stresses on the link trunnion bearings when running
forward.
Before proceeding with the details of the gear, the
stroke of the piston, lap and lead, virtual eccentric
throw, valve travel and the point of cut-off must be
shown. Of these the stroke, lead, valve travel and cut-
off are determined with respect to the size of engine.
It is advisable to add i/32-inch to the actually desired
lead to provide for wear of pins and bushings.
Lap.
When liead, cut-off and valve travel are given, the
lap is found by the Reuleaux diagram, Fig. 82.
VALVES AND VALVE GEARS
233
234
MODERN LOCOMOTIVE
A circle with a diameter equal to the travel of the
valve is drawn and on this diameter the same per-
centage as the desired cut-off percentage in the cylinder
is measured from "A" to "B." From "B" is drawn
/
A
\fx*=^
^^\G
c
\
\
/
y^
^v^
y^
^^f^f
x
•
K M^
— — " — I — T
"x^
\ \ \ ^
\
/A
^
/
\
V
^^
/
Fig. 82.
a perpendicular line which intersects the circle at "C."
O-C will be the cut-off position of the crank. With the
lead as radius and "A'' as center, draw a semi-circle
on the opposite side of the diameter to that of the loca-
tion of point "C." From the cut-off point "C draw
a line tangent to the lead circle and extend same until
VALVES AND VALVE GEARS 2^$
It intersects the valve circle at "D." O-D will be the
position of the crank when the valve starts to open.
Draw a line through "O" perpendicular to the line C-D,
which it will intersect at "E." The distance E-O will
be the required lap. The given lead may now be added
to the lap directly by drawing a line through "A"
parallel to line C-D which will intersect the extension
of line E-O at "F." O-F will be the lap and lead, or
the amount of motion to be imparted to the valve by
the combination lever.
It will be noted that the angularity of the main and
eccentric rods has some effect as to the exactness of
the cut-off points in front and rear ends of the cylin-
der. This layout will, therefore, give an approximate
average of what may be obtained in practice.
This method is equally applicable to the ordinary
double eccentric motion with shifting links when the
centers of the eccentrics are located at "A" and "C
with the crank at "K" for direct motion and outside-
admission valve or for inside-a3mission when the mo-
tion is transmitted to same by means of a rocker. For
inside-admission with direct motion or outside-admission
using a rocker, the crank is located at "H" for the
same eccentric position; provided, in all cases, that the
center line of the cylinder passes through the center
of the axle, otherwise their relation to the crank must
236 MODERN LOCOMOTIVE
be changed to suit the angularity of the main rod when
on the dead centers and the irregularity introduced
thereby divided between the two dead centers. In the
shifting link motion the link block will follow a convex
curve from "A" to "C" in reversing from one full gear
to the other, with increased lead toward central position
with open rods, and a concave curve with diminishing
lead toward center with crossed rods.
Returning to the Walschaert gear, we find that the
combined motion of the single eccentric and the crank
give an exactly equivalent result in full gear, but in
linking up, the effect on the motion of the valve, is
equivalent to a link block following the straight line
A-G from full forward to full backward gear, thus giv-
ing a constant lead E-F at all cut-offe.
Virtual Eccentric Throw— With Lap and Lead
Known.
The required throw of point "F" (Figs. 80 and 81),
being the final throw imparted by the crank E through
the link to the combination lever, may be termed the
virtual eccentric throw. It can be found either mathe-
matically or geographically by the following formulae,
and as per Figs. 83 and 84, respectively. In both fig-
ures the valve circle is indicated by No. 2 and the
virtual eccentric circle by No. 3.
VALVES AND VALVE GEARS
237
b =: for inside admission and
R— c
RVa^ c*
b =:= for outside admission valves ^
R+c .
where b = the radius of a circle with a diameter equal
/nsfc/e Admiss/on
R-c
Fig. 83.
Oofsich Admission
Fig. 84.
to the throw of point "f/' (Figs. 80 and 81), repre-
senting the eccentric throw which may therefore be
called the virtual eccentric throw.
R — the length of the crank =: J^ piston stroke.
a = the radius of a circle whose diameter is equal to
the valve travel.
c = the lap plus lead = distance 0-F in Fig. 82.
238 MODERN LOCOMOTIVE
Cambination Lever.
It is evident that the motion of any point on the
combination lever can be represented by a circle, as the
two connections to which the motion is imparted,
namely, "m" and "F" in Figs. 80 and 81 emanate from
two circular paths, the main crank "D" and the eccentric
pin "E" which is set at an angle of 90 degrees with
the former, providing that the link connection of the
eccentric rod is located on the center line of 'the engine
in its central position. Even if the link connection is
off the center line of the engine when the eccentrics
will be more or less than 90 degrees in the lead or fol-
lowing of the crank, the effect of the movement of point
"F" (Figs. 80 and 81) will be the same as if the eccen-
tric crank had exactly 90 degrees angle to the main
crank and consequently the line "b" in Figs. 83 and 84
will always be represented at right angles to the crank
With "O" as center of axle, lay out the length "R"
of crank "D." Through "O" draw a line perpendicular
to length "R" ; also with "O" as center draw the known
valve circle.
For inside-admission valves, the lap and lead "C* is
laid off from "O" toward the crank "P." From this
point draw a line perpendicular to D-0 until it inter-
VALVES AND VALVE GEARS 239
sects the valve circle (No. 2) at "f." From "D" draw
a line through "f" until it intersects the vertical diame-
ter of the circle at "h," when O-h or "b" will be the
radius of the vertical eccentric circle No. 3.
For outside-admission valves, Fig. 84, the lap plus
lead is laid off on the opposite side of *'0" to that of
the crank and a perpendicular line is drawn in the same
manner as in Fig. 83 until it intersects the valve circle
at "f." Where the line D-f intersects the vertical center
line of axle at "h," the radius "b*' of the virtual eccentric
circle is found by the distance O-h.
For outside-admission valve the eccentric circle will
always fall inside of the valve circle; but for inside-
admission the eccentric circle may fall inside of, on,
or outside of the valve circle, depending on the rela-
tions between the stroke, valve travel and lap and lead.
The length of the combination lever will be made to
suit the distance between the piston rod and valve stem,
but its proportions will be V : L ^ C : R. The point
of valve stem connection, measured from "m," will be
L — V for inside. Fig. 80, and L-fV for outside admis-
sion valves, Fig. 81, the valve stem connection falling
below the radius bar connection in the former case, and
above same in the latter case.
As a further illustration of how all the connecting
points on the combination lever can be represented by
240 MODERN LOCOMOTIVE
circles, refer to Fig, 85 for inside, and Fig. 86 for
out si de-ad miss ion valves which makes the whole system
clear and complete. In these figures the swing of the
L'l
Fig. 85.
lower end of the combination lever is represented by the
crank circle "i" from which it receives its motion.
On the same center is drawn the valve circle "2," the
virtual circle "3," the lap-plus-lead circle "4," and the
VALVES AND VALVE GEARS
lap circle "5." Tangent to lap and lead circle "4" is
drawn a line f-f perpendicular to the crank O-D until
F1G.86.
it intersects circle "2" at "f." By drawing the line
D-f, extended to the transverse center line of the axle
"O," it will intersect the eccentric circle at "h," which
is in this respect a repetition ot that found in Fig. 83
242 MODERN LOCOMOTIVE
Fig. 86 gives the same arrangement, but for outside-
admission, except that the Hne f-f is drawn tangent to
the lap and lead circle on the opposite side of the axle
"O" to that of the crank and the line D-F is drawn
intersecting the transverse center line at "h," as in
Fig. 84.
Length of Radius Rod.
With due consideration of the length of the eccentric
rod, the radius rod should be as long as circumstances
will allow. It is also subject to a minimum limitation
in length, and a minimum of three times the travel of
the link block ''g' from full "forward" to full "back"
gears is a good rule. See Figs. 80 and 81.
Link Slot Radius.
From the point of connection between the radius rod
and the combination lever as center, strike off the link
slot with a radius equal to the length of the radius rod.
Link Fulcrum.
At the same distance and on the same side above or
below the extended center line of the valve stem as the
average distance of the radius rod connection (point
"F"), is the preferable location of the fulcrum of the
link "O," Figs. 80 and 81. With a reasonably long
radius rod a slight deviation from this will have little
or no detrimental effect on the movement of the valve.
VALVES AND VALVE GEARS ^43
Swing.
The angular swing of the link should never exceed •
45 degrees, preferably 40 degrees, from one extreme to
the other.
Link Block Movement.
Full "forward'' and full "back'' positions of the link
block "g," Figs. 80 and 81, will be at a point on the
link where the swing is equal to the diameter of the
virtual eccentric circle whose radius is "b," Figs. 83 and
84.
Throw of Eccentric Pin.
Determine the actual throw of the eccentric pin "E"
by the relation of the location of the link block "g"
in full gear, Figs. 80 and 81, to that of the eccentric
rod connecting pin **M" from the link fulcrum. Gen-
erally the eccentric pin "E" will have two or three times
greater throw than the virtual eccentric motions of
points "g" and "F."
Len^h of Eccentric Rod.
Make the eccentric rod E-M as long as practicable,
using three times the actual eccentric throw of pin "E"
as a minimum length.
244
MODERN LOCOMOTIVE
Ecoentric Rod Connectioii to Link.
• special attention must be given to the location of the
connection of the eccentric rod with the link pin at
point "M" in Figs. 80, 81 and 87. This location must
be plotted out because of the irregularity due to this
Fra 87.
point "M" generally being some distance above the cen-
ter line of the engine and also because of the angularity
of the eccentric rod. The normal angle of 90 degrees
between the crank "D" and the eccentric pin "E" must
be modified to suit the height which the link pin "M"
is above the center line of the engine and is determined
in connection with the fore and aft locations of the
pin "M." With limited lengths of eccentric rods, the
VALVES AND VALVE GEARS
MS
rear half of the eccentric circle gives a shorter throw
than the front half. To compensate for this, the pin
"M" will have to be moved back of the tangent of the
link, until it gives, by the upward rise in its rear throw,
the same angular swing to the link as that of the front
from its central position when the crank is at its dead
centers.
Fig. 88.
Great care should be exercised in locating this point
so that the natural irregularities, unavoidable in the
transmission of circular into lineal or oscillating mo-
tion, are properly compensated for in these particular
points to get a correct and satisfactory motion of the
gear as a whole.
*
Lifting Shaft Locatian.
The location of the lifting shaft "Q," Figs. 80 and
81, has an important bearing on the proper movement
246 MODERN LOCOMOTIVE
of the link block "g" and consequently on the move-
ment of the valve at all points between full forward and
full backward positions. The lifting arm connection "P,"
Figs. 80 and 88, at upper end of the lifting link, should
follow as near as possible a circular path described by
the upper end of the lifting link in a position perpen-
dicular to the radius bar while the link block "g" is
moved from one extreme position to the other, with the
main crank "D" at one of its dead centers, or being
the same as a circle drawn with "F" as center and a
radius equal to Vs'^+u^, where "s" is the length
F'-F of the radius bar and "u" the length of the lifting
link F'-P. The arm P-Q must necessarily be shorter
than the radius thus obtained, and the lift link shaft
"Q" should then be so located that with a convenient
length of this arm, the point "P" will describe a curve
intersecting the former at about 50 per cent cut-off
position of the arm in both front and back gears. If,
however, it is desired to favor the forward gear, a some-
what earlier intersection may be selected in the back
motion, when the forward half of the curve will coin-
cide more closely to the theoretical circle.
A somewhat closer refinement in this respect, is ob-
tained by the location of the lifting shaft on the center
line of motion back of link, Fig. 89.
VALVES AND VALVE GEARS 247
The back end of the radius rod being raised and
lowered by means of a sliding bearing, causes the link
block "g'' practically to follow the chord of the circular
path described by the point in the link determining the
throw of the block in all positions.
In the usual arrangement of the Walschaert valve
gear, the lead is constant and does not vary as the re-
verse lever is hooked up. The Walschaert valve gear
can, however, be so designed as to give a variable lead.
pi
Fig. 89.
There are many cases in which the variable lead is
preferred. With a variable lead, the longest possible
cut-off in starting can be obtained, combined with the
proper amount of lead at the ordinary running cut-off.
In the case of passenger locomotives particularly, a
steam distribution like this is often most desirable.
The favorable results for starting are, however, ob-
tained at the expense of the distortion of the valve
events in back motion. For this reason, the Walschaert
valve gear with variable lead is suitable only for pas-
248 MODERN LOCOMOTIVE
senger and fast freight locomotives ; and not for slow
freight and switching locomotives, and should there-
fore be used with discretion. This variation in lead is
accomplished by designing the combination lever for the
maximum lead in mid-gear and reducing it to a desired
Fig. 90.
minimum at full gear by shifting the eccentric era
in the proper direction until this occurs.
The general arrangement of the Walschaert valV)
gear depends largely on the general design of the locc
motive. Some of the ordinary forms of constructiot
of the various parts of the gear are shown in the follow;
ing illustrations.
VALVES AND \
249 I
Fig. 90 illustrates an eccentric crank and eccentric ,j
rod. The former is secured to an extension of the
main crank pin by a binding bolt. The eccentric crank
is split so that it can be drawn to a tight bearing by J
means of the holt. Thi.s bolt, together with a key, -
Fig. 91,
keeps the eccentric crank fixed in its position on the!
niain pin. It may be easily removed, if necessary, by J
driving out the biniling bolt. This construction has the I
advantage that it permits of using a solid bushing on-!
the side rod at the main crank pin.
Fig. 91 illustrates the link and reverse shaft. In the
design shown, the rai'.ius rod is directly connected to the
lift shaft ami by means of a slip block. In such a case,
V 250
H the
^H part
^M disco
^H make
1
1 the r
^1 St rue
H
H Com
H guid
■ It w
^m with
MODERN LOCOMOTIVE
everse shaft arm is made in two parts, the
being easily removable. This permits of r
nnecting the reverse shaft and radius rod
s a very simple arrangement,
another style of the reversing mechanism
nonly used, the arm of the lift shaft is connec
outer ^H
eadily: ^^H
alsoH
ed t(^H
lotive^^l
erit^^j^^l
gear.^H
piec^<^|
de iB^^H
Fic. 92.
adius rod by means of a link. This type 0:
tion is shown in Fig, 92.
is figure ,ilso shows the American Locon
lany's latest patented arrangement of seif-cen
for the valve stem of the Walschaert valve
11 be noticed that the guide is cast in one
the steam chest head. Consequently, the gu
VALVES AND VALVE GEARS 2$!
L always central with the piston valve chamber. An
I arrangement of this kind has the advantage that it can
be erected, taken down and replaced without any lining
L np. The guides are so constructed that they can be
I «sily adjusted for wear by means of liners. This
Fig. 93.
arrangement also permits the use of a straight design
of lap and lesd lever without forks. The lever is con-
I nected to the valve stem crosshead by a pin passing
I through its wings. In case it is necessary to take down
V the lap and lead lever, the upper portions of the guide
I may be removed by taking out four bolts. This gives
;ss to the pin connecting the lap and lead lever to
I the crosshead.
252 MODERN LOCOMOTIVE
Fig. 93 illustrates the latest arrangement of the com-
bination link directly connected to the wrist pin. This
arrangement has the advantage of eliminating the cross-
head arm and bushing, thereby reducing the number of
parts and also reducing the reciprocating weights. It
also simplifies the construction of the guide yoke end.
However, on long stroke engines, the pins are so close
together that a good arrangement is not practical.
In Case of Accidents.
Having considered the principles and construction of
the Walschaert valve gear, the next phase of the sub-
ject to take up is what should be done in case of acci-
dents. This is of the utmost interest to all engineers.
It would be impossible to lay down rules to cover every
case that might arise. It is possible, however, to con-
sider some of the more usual or most possible accidents ;
and determine the best and quickest courses to follow
in such cases.
The accidents to be considered may be divided into
two general classes; those in which it is not necessary
and those in which it is necessary to block the valve to
cover the ports.
The first class of accidents includes only those cases
in which it is necessary to take down the main rod.
The valve must necessarily be blocked if the main rod
is disconnected.
VALVES AND VALVE GEARS 253
In the second class of accidents, the damage to the
machinery may or may not make it necessary to take
down the main rod.
Blain Rod Up, Valve Not Blocked.
The following is considered a good rule to follow in
regard to taking down the main rod. When it is possible
to lubricate the cylinder and relieve compression, other-
wise than by removing the cylinder cocks, the main rod
may be left up if in a condition to run. For example:
if there are relief or vacuum valves in the cylinder
heads, these may be removed. This will prevent com-
pression and also permit of lubricating the cylinder.
Considering the first of the above mentioned classes
of accidents in which the valve does not have to be
blocked ; suppose, for example, an eccentric crank, eccen-
tric rod or the foot of the link is broken.
Fig. 94 illustrates how the valve • gear may be dis-
connected in such cases. Take down the eccentric rod,
disconnect the radius rod from the lift shaft and secure
the link block in the center of the link. The valve on
the lame side then receives a motion irom the lap and
lead lever. Its travel will be equal to twice the total
amount of the lap plus the lead. This gives a port
opening equal to the amount of the lead. Consequently,
the main rod may be left up, as the cylinders will be
lubricated. Furthermore, though the cut-off on the
VALVES AND VALVE GEARS 255
disabled side will be very short, the steam that is
admitted will do a certain amount of work, and the en-
gine can be reversed.
The link block may be secured in the center of the
link by means of two blocks wedged in position, as
shown in the illustration.
With the link block thus secured, care must be taken
not to come to a stop with the main pin on the lame
side on either quarter. In such an event, the lap and
lead lever would be in a' perpendicular position, or ap-
proximately so; and the valve would be practically cen-
tral on its seat. As the crank pin on the other side
would be on a dead center, it would, thus, be impossible
to start the locomotive.
In Fig. 94 the radius rod is connected to the lift shaft
arm by means of a link or hanger. It can thus be readily
disconnected.
When the radius rod is directly connected to the lift
shaft arm by means of a slip block as shown in Fig.
95, the reverse shaft arm is made in two pieces. To
disconnect the radius rod, it is necessary only to re-
move the outer section of the lift shaft arm and remove
the slip block.
Considering the second general class of accidents:
those in which the valve has to be blocked to cover the
ports. This class, as already stated, may in turn be
VALVES AND VALVE GEARS 257
divided into two other classes: First, cases where it
is necessary to take down the main rod; second, those
in which the Imain rod is in condition to run. In the
latter cases, the rules governing what is considered good
practice as to leaving the main road up or taking it
down has been previously given.
Taking up these two kinds of accidentS^ in their order :
Blain Rod Down, Valve Blocked.
Assume that the main rod is broken or the piston rod
bent. In the case of the inside-admission valves, the lo-
comotive may be disconnected and blocked as shown in
Fig. 95. Disconnect the radius rod from the lap and
lead lever. Suspend it clear of the latter. Secure the
valve to cover the ports. This can usually be done by
means of a set screw provided for this purpose. In
the design illustrated, the set screw will be noticed on
the side of the valve stem guide. If no set screw is
provided, a valve stem clamp is usually included in the
tool equipment. Clamp or block the crosshead at the
back end of the guides as shown.
With the valve motion disconnected in this way, the
reverse lever is free to operate the other side; and the
locomotive can be run in on one cylinder.
If the crosshead arm, lap and lead lever connector,
or lap and lead lever is broken, the same method may
be followed. Of course, such of the broken parts as
VALVES AND VALVE GEARS 259
would in any way interfere with' running the locomotive
would have to be removed.
In the case of outside admission valves, the same
course may be followed as illustrated in Fig. 95, and
described above ; except that the lap and lead lever must
be taken down. If this was left up, the radius rod
would strike it as the latter moves back and forth to
the motion of the link.
Main Rod Up, Valve Blocked.
In such a case, if the valve has inside admission, the
locomotive might be blocked as shown in Fig. 96. For
example: suppose the lap and lead lever, lap and lead
lever connector, or crosshead arm was broken. Discon-
nect the radius rod from the lap and lead lever. Sus-
pend it clear of the latter. Tie the lower end of the
lap and lead lever ahead to clear the crosshead on the
forward stroke. The locomotive can then be run in on
one side.
If the valves have outside admission: under condi-
tions similar to those assumed in the case of Fig. 96,
the lap and lead lever must be taken down. In other re-
spects, the same method may be followed.
When the radius rod is suspeAded, a chain or wire
should be used. A rope would be quickly cut through
by the motion of the radius rod.
26o MODERN LOCOMOTIVE
Setting the Walschaert Valve Gear.
If the gear is properly designed, the setting of the
Walschaert valve motion is very simple.
It is essential that the length of the eccentric crank,
the lengths of the arms of the lap and lead lever and the
length of the lap and lead connector should check ex-
actly with the drawings. No change from the drawings
in any of the above parts should be made.
Assuming that all the parts check with the drawings,
any adjustments which may be necessary to square the
motion should be made in the lengths of the eccentric
rod, radius bar or valve stem.
Diagrams "A" and "B," Fig. 97, illustrate, respec-
tively, the effects on the position of the valve resulting
from changes in the lengths of the radius rod and eccen-
tric rod.
It is apparent from diagram "A" that any change in
the length of the radius rod "R" will have a corres-
ponding and practically equal result on the position of
the valve. That is, if the radius rod is lengthened
%-inch the valve will be moved forward on its seat
a like amount, or vice versa. Therefore, to move the
valve ahead or back any amount, lengthen or shorten
the radius bar respectively a like amount.
Reference to diagram "B," Fig. 97, shows that the
effect of a change in the length of the eccentric rod
VALVES AND VALVE
GEARS 261
262 MODERN LOCOMOTIVE
on the position of the valve depends on whether the
link block is in the top or bottom of the link. The fol-
lowing rules therefore govern:
When forward motion is taken from the lower half
of the link.
In forw&rd motion: To move the valve ahead,
lengthen the eccentric rod. To move it back, shorten
the eccentric rod.
In backward motion: To move the valve ahead,
shorten the eccentric rod. To move it back, lengthen
the eccentric rod.
When forward motion is taken from the upper half
of the link.
In forward motion: To move the valve back,
lengthen the eccentric rod. To move it ahead, shorten
the eccentric rod.
In backward motion: To move the valve ahead,
lengthen the eccentric rod. To move it back, shorten
the eccentric rod.
A change in the length of the eccentric rod will not
alter the position of the valve a like amount. The two
will have approximately the same ratio to each other as
that between the eccentric crank throw and the. valve
travel.
For example: Suppose the eccentric throw is 12
inches and the valve travel 6 inches. The ratio is two
VALVES AND VALVE GEARS 263
to one or the latter is one-half of the former. In such
a case, a change in the length of the eccentric rod of
%-inch would alter the position of the valve only one-
half of that amount, or i/i6-inch.
The following method of setting the Walschaert valve
gear is equally applicable to designs having constant
lead and those having variable lead.
First: Check the lengths of the eccentric crank, the
lap and lead lever, and the lap and lead lever connector.
These dimensions should conform to the drawings and
should not be altered.
Second: Raise the main wheels so that the distance
from the center of the wheel to the top of the frame
conforms to the amount specified, minus J^-inch for
wear of brasses. Then find the dead centers and port
marks in the usual manner.
Third: Assemble the gear complete, temporarily
tightening the eccentric crank in a position which will
give the specified throw.
Fourth: Place the radius bar in the center of the
link. Mark the mid-gear position. Then get the lead
at each end of the cvlinder. When the lead is con-
stant, the average lead, or the sum of the leads on oppo-
site ends divided by two, should be equal to the specified
lead in full gear. When the lead is variable, the average
lead in mid-gear position should be equal to one-half of
264 MODERN LOCOMOTIVE
the sum of the specified leads in full forward and full
back gear. In other words, it should be the lead due
to the lap and lead lever, unaffected by the position of
the eccentric crank. Any error in the average lead when
the radius bar is in central position is due to an error
in the length of the upper or lower arms of the lap
and lead lever.
Having thus checked the lengths of the lap and lead
lever, equalize the lead by means of the adjusting nuts
on the valve stem or by changing the length of the
radius bar.
Fifth: Drop the lever into forward gear until the
specified travel is obtained. Then, if the average lead
is equal to the specified lead in full gear, the eccentric
crank is correctly set. If this is not the case, the eccen-
tric crank should be driven one way or the other until
the error is corrected. If the average lead is less than
the specified lead, the eccentric crank should be driven
inward, if it leads the main pin; and driven outward,
if it follows the main pin. If the average lead is more
than the specified lead, the eccentric crank should be
driven outward, if it leads the main pin; and driven
inward if it follows the main pin.
After eccentric crank is correctly set, check valve
travel ; and relocate full forward position of the reverse
lever.
VALVES AND VALVE GEARS 265
Sixth: If the average lead is correct but unequally
divided on the front and back centers, lengthen or
shorten the eccentric rod, according to the rules given
above, until it is equalized. It must be borne in mind
that to change the lead a given amount the eccentric
rod must be changed a greater amount, or about in
proportion as the eccentric throw is greater than the
valve travel. (See Fig. 97.)
Place the reverse lever in a position that will give
full travel to back gear, marking this position on the
quadrant ; and check the lead in the same manner. With
variable lead, the full back gear lead should be as much
greater than the lead at mid-gear as the lead at mid-
gear is greater than that at full forward gear.
Seventh: Run over the cut-offs and obtain other
events for as many positions as required. In running
over the cut-offs of locomotives of the articulated type,
obtain the cut-offs for each position of the lever for
both engines before moving the lever to a new position.
This is necessary in order that the relative cut-offs in
high and low pressure cylinders may be compared.
Note: Do not attempt to square cut-off at the expense
of lead and port opening.
Variable Lead.
When this setting is resorted to, it is advisable to
adjust the gear according to the general rule, using a
266 MODERN LOCOMOTIVE
temporarily fixerl eccentric crank to obtain the proper
length of the eccentric rod and valve location, after-
wards, readjust the eccentric crank to suit the desired
lead in full gear.
The Kingan-Ripken Valve Gear Device.
A simple and practical device, designed to overcome
the slow action the combination lever imparts to the
Walschaert, and similar valve gears, was patented
April i6, 1912, by James B. Kingan and Hugo F.
Ripken, of Minneapolis, Minn.
This device is the result of considerable study and
experiment in an effort to overcome the slow starting
of trains, and maintenance of speed, by engines equipped
with the Walschaert valve gear, which is due to the
heavy constant lead required at short cut-oflfe, in order
to maintain sufficient port opening, where little open-
ing other than that transmitted by the combination lever
is given to the valve. This constant lead is too ex-
cessive for the maximum cut-off, and the starting of
a train, and, as it requires one-half the movement of
the crosshead in order to overcome the lap and lead,
has a tendency to slow the action of the valve gear, as
ordinarily connected.
This arm, in addition to receiving the usual cross-
head motion, also receives a supplementary motion from
VALVES AND VALVE GEARS 267
the main rod, for now being attached directly to the
main rod, it receives the same oscillating movement the
rod does from its pivot, the wrist pin.
And the fact that the largest part of this movement
is transmitted to the combination lever as the crosshead
approaches and recedes from the end of its travel, causes
it to give to the combination lever an entirely different
movement from that transmitted by the usual orosshead
connection.
This movement, as shown in the illustration, causes
(as the piston is on the last half of its stroke) release,
compression, and pre-admission to occur later in the
stroke with the same cut-off, thereby giving a longer
period of expansion, less compression, and through the
fact that the supplementary motion transmitted is the
greatest just as the crosshead approaches and recedes
from the end of its travel, there is a great deal less
pre-admission with the same amount of lead. The piston
having reached the end of its travel, the main rod is
now in the center of its oscillatory movement and the
device has therefore no effect upon the lead. But as the
piston leaves the end of its travel and the main rod
again assumes an angle, a quicker, larger and longer
maintained port opening is obtained with the same cut-
off and also a longer cut-off with the reverse lever in
the same notch, or position. By placing the combina-
268
MODERN LOCOMOTIVE
tion link connection in this device in such a position
as to take advantage of the various angles that may be
transmitted to the combination link, through its use a
much more even distribution of steam is obtained in the
cylinders.
Later release and compression, less pre-admission, a
quicker, larger and longer maintained port opening with
Fig. 98.
the same cut-off, and more uniform valve events, allow
the use of a shorter cut-ofF wth its constant saving of
steam, and this fact, combined with the longer maxi-
mum cut-off obtainable, makes it absolutely certain that
a quicker starting, faster, more powerful and more
economical engine is obtained.
DESCRIPTION OF OPERATION.
A full conception of the device may be had by refer-
ence to the accompanying illustration. When the cross-
VALVES AND VALVE GEARS 269
head is approaching the forward center and the main rod
is in an inclined position, the arm being rigidly attached
to the main rod, its bottom end, or union link con-
nection, is the same degree back of the pivot point (the
wrist pin) as the main rod is above it. The combination
lever, being connected by means of the union link to
the bottom end of the arm, has its action delayed in the
same proportion.
The events of release, compression and pre-admission,
taking place in this part of the stroke, are delayed pro-
portionally with the delayed action of the combination
lever.
Referring to Fig. 98 it will be observed that the cross-
head having reached the end of its travel in this posi-
tion, the main rod is in the center of the oscillatory move-
ment derived from the wrist pin, and no movement be-
ing transmitted to the combination lever other than that
given by the crosshead, the combination lever is there-
fore in the same position it would occupy if connected
directly to the crosshead. Lead is therefore not affected
by the use of this device.
Following the position shown in Fig. 98, the cross-
head commences its return stroke, and the main rod,
having passed its pivotical center, is again in an inclined
position, and has moved the bottom end of the arm ahead
of the position it held in relation to the crosshead while
2";*} MC'DERX U>O0MOm"E
on center, and *n >c» ■X'infr has delaved the return move-
men! of the combination lever.
'\\v: 'ori binati^^n lever traveling in a direction opposite
to that of the ra<!ius rod which is opening the valve
port in this position, Avould greatly tend to slow the
action iA the valve j:rear. But this device, in dela\'ing
tlic rttnrn movement of the combination lever, gives to
the valve a fjiiicker. larjjer and longer maintained port
opeiiin.Lr witli tlie same cut-oflF, and a longer cut-off with
the rcv<r^e lever in the same position, than the Wal-
M-hacrt or any other valve gear using the combination
liv«-i can ;;^ive. with th< old style crosshead connection.
The invention is marketed by Mudge & Company,
< hi( a;'.n, III.
Davis Variable Lead Attachment.
'I'lif <l<'vicc herewith presented for consideration was
p.itcnic«I Direinher T), 1910, by Mr. William Lynn Davis,
lo whniM wc are indehted for the following description:
"'I'ni maii\ years there has been a desire of locomotive
i|iMi;iicis t«) nhtain a variable lead valve gear showing a
'.tcnii dish ilmt inn c(|nally as ^ood as the Stephenson but
whiih wniiM rinhody in its design the accessability and
the MMipMcity K\\ the Walschaert.
In cunsideralinn of this, the valve gear embodying the
h.iNi*. v.u iahle lead attachment was designed, as shown
in I he .icmiHpanyiiiL; illustration, to give a variable lead
VALVES AND VALVE GEARS 2^\
increasing as the link block travels from the ends of the
link toward the center, or, as the engine is "hooked-up,"
and vice versa, giving the valve gear its proper and most
efficient movement at the beginning of the stroke both
in full gear and in the cut-off, thus making it especially
beneficial in starting on account of leaving the engine
free of all preadmission, lengthening out the cut-off, and
also delaying the exhaust. In other words, it has been
demonstrated that an engine with the Davis attachment
whose cut-off in full gear before the attachment was
applied was 21 inches, was 23^ inches after the attach-
ment was applied, showing an increase of 2^ inches in
the distance that the steam followed the piston, and de-
laying the exhaust occurrence when the piston was within
13^ inches of the completed stroke; this, of course, aidr
ing greatly in starting the engine. By means of this
attachment any desired lead can be obtained at two
points, in the cut-off and at full gear, without any change
in design.
Further: In the Walschaert type of valve gear the
location of the pivot connection joining the lap and lead
lever and the radius rod determines the amount of valve
lead, and it is a difficult operation to locate this pivot at
the most desirable point, frequently involving many ex-
pensive trials and requiring the reconstruction of the
lever or the making of new ones. When the most de-
2^2 MODERN LOCOMOTIVE
sirable location has been found, to suit the usual condi-
tions arising in the running of a locomotive, the distribu-
tion of the steam is still faulty and ineconomical, the
best results in steam engine practice being obtainable
only by varying the lead in relation to the cut-ofF so
that as the main stroke of the valve decreases, the lead
increases, and vice versa. In the Stephenson link mo-
tion the variation of the lead is accomplished by the
combination of the motions received from the two ec-
centrics set at relatively different positions to the crank,
pin and the rotation of the strap and link around the
eccentrics as the link is raised or lowered. The prin-
cipal advantage of the Davis attachment is to provide
means for easily varying the relative lengths of the arms
of the lead and lap or combination lever, with the Wal-
schaert type of valve gear, whereby the valve lead may
be easily varied. In making the pivot joint moyable
its location may be easily and readily altered or changed
through a range which will vary the lead from the great-
est to the least desirable amount under the conditions
existing at different times. Now if this change can be
accomplished automatically without interfering with or
adding to the duties of the engineer, the principal ob-
ject has been obtained.
In designing the valve gear illustrated here it will be
noticed that the distance between the two upper pins in
VALVES AND VALVE GEARS
273
the combination lever is subject to change through a U
hanger and a bell crank, the latter being connected to
the hanger pin on the tumbling shaft by the main con-
necting rod, or, as it has been named, the lead and lap
adjusting rod.
In other words, the main advantage of the Davis
attachment for the Walschaert and kindred types of
Fig. 99.
valve gears resides in the combination of the lead and
lap lever and the radius rod with the shif table fulcrum
pin, by which the lead and lap lever and radius rod are
joined, and means for shifting this fulcrum in order to
automatically vary the action of that part of the valve
mechanism which produces the lead, when the reverse
lever is moved to adjust the cut-off. Fig. 99 simply illus-
trates the valve gear as designed to cover the Atlantic
type of balanced compound passenger engine in use since
274 MODERN LOCOMOTIVE
i()i2. on the Atchison, Topeka & Santa Fe Railway. It
is readily understood that the details, in order to be ap-
plicable to other valve gears of this type than the Wal-
schaert, can be modified or altered to accommodate the
construction of that particular valve gear. From the
accompanying ilhistration it will be noticed that the valve
gear in general is of the ordinary Walschaert type,
except the upper end of the combination lever, which is
bifurcated and the front end of the radius rod, which,
instead of being pinned directly to the combination lever,
has trunnions on its front end which carrv blocks, the
blocks in turn sliding in the jaws provided on the inside
faces of the combination lever. The combination lever
carries on its outer faces bosses which engage in the
rocker arm, which, in turn, moves the valve. It is read-
ily seen that if the engine were ''hooked-up" from the
position in which it is shown in the illustration, the
upper radius rod hanger pin would come more nearly in
a line with the center of the tumbling shaft and the
upi)er end of the bell crank, which would tip the bell
crank forward, thereby pushing down the U hanger and
with it the trunnioned end of the radius rod, increasing"
the distance between the centers of the pivot connec-
tion on the radius rod and the rocker arm connection,
thus increasing the lead.
VALVES AND VALVE GEARS 275
It has been demonstrated time and again that the
Walschaert valve gear makes an engine a poor accel-
erator and engines equipped with that gear have given
trouble in starting trains; especially heavy trains which
require the maximum tractive effort; also local passen-
ger trains where rapid acceleration is of prime import-
ance. The application of the Davis attachment is low
in cost and it does not in any way destroy the accessi-
bility feature of the Walschaert gear. It adds little to
the complexity and will make any Walschaert valve gear
more economical and flexible and will make an engine
employing it a far better accelerator."
Mr. Davis is at present employed as a Mechanical
Engineer by the Interstate Commerce Commission, at
Kansas City, Mo.
THE BAKER VALVE GEAR.
The original Baker valve gear for locomotives was the
joint invention of Mr. Abner D. Baker, of Swan ton,
Ohio, and Mr. Charles J. Pilliod, of Angola, Ind., and
an American patent on the valve gear was issued No-
vember 3, 1908.
This form of valve gear was primarily designed for
traction engines, and was originally known as the Baker-
Pilliod valve gear, but during 1908 it was first applied
to a locomotive and passed through the experimental
276 MODERN LOCOMOTIVE
state, or period, of development covering about two
years.
In 1 910 the gear was entirely remodeled, and some
organic changes were made in its mechanical construc-
tion, which increased its efficiency and stability to a con-
siderable extent. As a whole, the gear is now more
accessible and compact, weighs less, and can be more
easily applied.
The driving force of this valve gear is, like the
Walschaert, derived partly froni the eccentric crank and
partly from the crosshead. In this respect the two gears
are similar. The most important distinction between
the two types is the absence of a fixed, or shifting,
radial link in the Baker, as may be seen in Figs. 103
and 104, and its employment in the Walschaert. The
reverse bars and reverse yoke, used in the Baker valve
gear, take the place of the link used in the Walschaert
and Stephenson valve gears.
The combination lever of both types of gear move the
valve the amount of lap and lead in each direction,
while the balance of the valve travel is obtained from the
eccentric crank. In the Baker gear the eccentric crank
transmits its motion through the eccentric rod to the
gear connecting rod, radius bar, bell crank and valve
rod, dispensing with the oscillating radial link, link
block, and radius bar, employed in the Walschaert gear.
VALVES AND VALVE GEARS
278 MODERN LOCOUCPTIVE
und iliiis avoids the usual variation occasioned by the
slip uf the link block.
Description.
The Baker valve gear is an outside gear having no
links or t-cccntrics. The bearings of all moving parts
SECTraH AT KLL CRANK
are pins and bushings, making it easy to repair. The
movement of the valve is controlled by the reverse yoke,
shown in Figs. loi and 102, which is pivoted in the
gear frame. This reverse yoke carries the radius bar,
on the lower end of which is pivoted the gear con-
necting rod. This gear connecting rod extends from
the radius bar bearing downward to connect with the
eccentric rod and upward to connect with the bell crank.
VALVES AND \
279
The minimum vertical movement of the gear connect-
ing rod is obtained with the reverse yoke in mid-gear,
and, as the reverse yoke is moved toward either extrem-
ity, the valve travel is increased through the increased
oscillation of the bell crank, by means of a greater ver-
COMnNATIONLKVUI
ECCENTNIC ROD
Fig. 102.
tical movement of the three gear connecting rod bear-
ings.
A movement of the lower end of the gear connecting
rod. Fig. 102, to the left, with the reverse yoke in
forward motion, produces a lifting action of the gear
connecting rod, which moves the valve back by revolv-
ing the bell crank clock-wise. This same movement of
28o MODERN LOCOMOTIVE
the lower end of the gear connecting rod will produce
a falling action of the gear connecting rod with the re-
verse yoke in the back motion, which reverses the move-
ment of the bell crank and valve. The crosshead con-
nection moves the valve the amount of lap plus lead in
each direction. This makes the lead constant) and in-
dependent of the cut-off.
Application.
This valve gear may readily be applied to all modem
equipment, either old or new, and to any class of service.
There is but one type of gear for inside steam distri-
bution, shown in Fig. 103, and one for outside steam
admission locomotives, illustrate^l in Fig. 104. They are
applicable and interchangeable for all classes of service.
ADVANTAGES.
The Baker, like other outside valve gears, has numer-
ous advantages over inside valve gears. Being located
outside, it relieves the complexity and congestion under-
neath the engine and permits practical bracing of the
locomotive frames. The gear is standard in all parts,
regardless of size or class of engine.
After setting, the valve gear keeps its adjustment per-
manently. Having no links, eccentrics, or sliding blocks,
there is no chance for variance, as there is in the ordi-
nary link gear.
VALVES AND VALVE GEARS 281
1
1
\1
m
jJjI' \(
IT'
n-^
MODKHN LOCOMOTIVE
VALVES AND VALVE GEARS 283
All parts of the gear are easily accessible, making
inspection easy and renewals when necessary after long
service, inexpensively and quickly made. Every mov-
ing part is equipped with an integral oil well, thoroughly
protected from dust and dirt, insuring positive lubrica-
tion. The points where wear occurs are all bushings
and pins, very quickly and easily replaced, bringing the
gear into its original alignment and proper relationship
with the valve. This is not obtainable with some other
gears where bushing points are independent of the loco-
motive, or where wear or distortion of the link, or the
block, will disturb the steam distribution. A more uni-
form cut-off and release is obtained and therefore greater
effective expansion from the steam.
Few repair parts must be carried in stock, for several
parts will fit either right or left or both inside and out-
*
side admission gears, and most of the other parts are
interchangeable right and left. In making replacement
of worn or damaged parts on the Baker gear, all that is
necessary is to remove a couple of nuts and pins, slip
the stock part in place, and the engine is again ready
for service.
Setting the Baker Valve Grear.
Assemble the valve gear in accordance with the de-
sign furnished. Valve travel, lap, lead and exhaust
clearance are shown on assembling design.
284 MODERN LOCOMOTIVE
It is essential that the length of the eccentric crank,
combination lever arms, union link, and valve stem
check with drawings.
Clamp the eccentric crank temporarily to the main
pin, and locate as near as possible to the specified throw.
Locate the dead centers in the usual way. Place the re-
verse lever in full forward motion position, while locat-
ing the dead centers. In doing this full travel, lead,
and all clearance can be tested, and, in a great many
instances, sufficient information can be obtained from
the marks that have been made on the valve stem from
original adjustment as will enable the valve setter to
make alterations with one complete revolution of the
wheels.
Eccentric Ctank Setting.
With the engine on the front dead center, tram. from
the center of the pin in the front end of the eccentric
rod to any stationary point, such as the guide yoke or
guides, as shown by the tram points *A' and *B' in
Fig. 100. (In most cases the wheel tram can be used for
this work.) After scribing a line across the side of
the main guide or guide yoke end with the 'A' end of
the tram, revolve the wheel to the back dead center,
and scribe the guide or guide yoke end again; if these
two lines are together the crank setting is correct. If
they are not, move the eccentric crank in the required
VALVES AND VALVE GEARS 285
direction until these lines come together. The position
of the reverse lever is not important while finding the
eccentric positions. The eccentric crank always follows
the main crank pin.
Eccentric Rod Length.
The inside admission valve gear is direct in forward
motion and indirect in back motion. The ratio of the
valve gear is about 4 to i ; therefore, the valve will move
forward 1/16 inch if the eccentric rod is lengthened J4
inch, with the reverse lever in extreme front stroke po-
sition and the crank pin on front dead center. With the
reverse lever in extreme back stroke position and the
crank pin on back dead center, the valve will move back
1/16 inch when the eccentric rod is lengthened J4 inch.
Having taken the port marks with standard valve stem
tram, the object is to square the lead in forward and
backward motion on front and back dead centers.
Changes necessary on the eccentric rod and the valve
rod are determined from lead marks.
Let us take a valve with 14 inch lead, showing a dif-
ference between front and back motions of % inch,
making it necessary to move the valve backward 1/16
inch to square the forward motion lead with the above
ratio, 4 to I, the eccentric rod must be shortened J4
inch. On inside admission gears the direction of the
change in the eccentric rod should be the same as that
286 MODERN LOCOMOTIVE
in which the valve should move to correct the forward
motion.
Do not try to square cut-offs by squaring the port
opcnini^ in full Q^ear jx^sition, as, in the Baker gear, the
back port o])cning is larger than the front. This should
l>e (lone with reverse lever at 50% cut-off position.
The foregoing a])plies to inside admission only, and
any alterations in the eccentric rod length are just the
opposite for outside admission valves.
CL'T-OFF AND ECCENTRIC ROD.
The following rule will determine whether or not the
eccentric rod is of the correct length: If the cut-offs
are long on the front end in forward motion and long
on back end in backward motion, the eccentric rod is
too long. If the cut-offs come just the opposite of the
foregoing, then the rod is too short. Valve setting may
be considered correct when there is not more than Y^
inch difference in the piston and cut-offs.
Valve Travel.
Place the reverse lever in full forward position and
test the full valve travel shown on the drawings. Due
care should be taken to see that the reach rods, are the
same length as shown on the drawings. If there is a
difference between the right and left sides of the en-
VALVES AND VALVE GEARS 287
gine, change the gear reach rod on the side of the en-
gine where the short travel exists. After obtaining equal
travel on each side of the engine in this manner, the
reverse lever should be put in its central position and
the main reach rod adjusted. Then- the reverse lever
quadrant length, or power reverse cylinder crosshead
guide should be tested for the desired travel in both full
forward and back motions. The full gear position of
the reverse yoke for inside admission should not be less
than 5}i inch from the bell crank pivot, in the forward
motion, and not greater than 2oj4 inches in the back
motion. With outside admission gear, this dimension
for the forward motion position of the reverse yoke
should not exceed 20j4 inches, and not less than 6j4
inches in the back motion.
Eccentric and Valve Rod.
Place the engine on each of the four dead centers in
full gear, both motions, and, with the valve stem tram,
make the lead marks on the stem. The changes neces-
sary on the eccentric rods and valve rods are determined
by the lead marks, just obtained, by the following pro-
cess. On inside admission gears the direction of the
change in the eccentric rod should he the same as that
in which the valve should move to correct the forward
motion.
288 MODERN LOCOMOTIVE
The eccentric rod adjustment is determined first, as
follows: Subtract the smaller lead on one end from
the larger on the same end and multiply the result by 2.
The valve rod error is determined as follows: Add
the two leads on one end and the two leads on the other
end, substract the smaller sum from the larger sum,
and divide the result by 4.
The change in the valve rod is always in the direction
of the greatest error. In the outside admission gear the
eccentric rod change is made in the direction opposite to
which the valve should move to correct the forward mo-
tion; otherwise the valve setting is the same.
Variable Lead.
When this setting is resorted to, adjust the valve gear
the same as described for constant lead, except that the
eccentric crank should be set accurately to the throw
specified, and moved from that location only if the spec-
ified lead variation is not produced. It should be dis-
tinctly borne in mind that no adjustment of the eccen-
tric crank can increase or decrease the total lead. With
any change by that method, the lead in one direction is
always obtained at the expense of the opposite motion.
To give more lead to that direction of rotation in which
the eccentric crank follows the crank pin the eccentric
crank should be moved outward from the journal, or
eccentric crank should be shortened, and in the reverse
VALVES AND VALVE GEARS 289
direction, just the opposite. Having adjusted the eccen-
trie crank location, eccentric rod length and valve rod
length by the methods just explained, the 'valve setter
should adjust the quadrant stops and reach rods to pro-
duce the specified maximum valve travel in each direc-
tion.
The cut~oflF should also be measured in at least one
position of the reverse lever in each direction.
IN CASE OF ACCIDENTS.
The breakdowns most common to the Baker valve
gear may be summarized as follows:
First — Those in which the main rod may be left in
position without blocking the valves.
Second — Those in which the main rod is taken down
and the valves must be blocked.
Third — Those in which the main rod may be left in
position and the valves must be blocked.
With the main rod in position, it is necessary to have
lubrication for the piston, and to relieve all compression
in the cylinder, in another manner than by removing
the cylinder cocks; that is, if there are relief, or vacuum,
valves in the cylinder heads, these may be removed.
This will prevent compression and also permit lubrica-
tion.
290 MODERN LOCOMOTIVE
MAIN ROD IN POSITION AND VALVE NOT BLOCKED.
Suppose, for example, one of the followers are broken ;
an eccentric crank, eccentric rod, radius bar, reverse
yoke, or upper end of the bell crank. Take down the
eccentric rod and other broken parts, disconnect gear
reach rod ; block the lower end of the bell crank by using
a U-bolt. This applies only to engines with the type
shown in Fig. 104. The valve on disabled side then re-
ceives motion from the combination lever and the union
link.
MAIN ROD REMOVED AND VALVE BLOCKED.
Considering the second of the above mentioned acci-
dents : For example, the main rod is broken and piston
rod bent; it is absolutely necessary to block the valve.
Take down the main rod and remove the valve rod, se-
cure the valve to cover the steam ports, by a small set
screw in the side of valve rod crosshead guide, provided
for this purpose.
If no set screw is provided a valve stem clamp may
be employed. Clamp or block the main crosshead at the
end of the stroke, and proceed with engine on onq side.
MAIN ROD IN POSITION AND VALVE BLOCKED.
Regarding the third class of accidents : Let us assume
that the valve rod or vertical arm of bell crank is broken.
VALVES AND VALVE GEARS 2gt
Remove the valve rod and block the valve, as previously
explained. If the combination lever or union link are
broken, remove valve rod and tie the lower end of com-
bination lever to cle^r the main crosshead, or remove
the combination lever and block the valve.
With the above conditions care must be taken not to
come to a stop with the main pin on disabled side on
top or bottom quarter, as the combination lever would
be perpendicular, and the valve would cover the steam
ports. The crank pin on the opposite side would be on
dead center, and it would thus be impossible to start the-
engine.
GEAR REACH ROD.
Should the gear reach rod break, block the reverse
yoke and wire it securely so that it cannot move; other-
wise, take down the eccentric rod.
MAIN REACH ROD.
Should the main reach rod break, block the reverse
shaft arms and wire securely, or block and wire the
reverse vokes.
In general, the best practice to follow, should any part
of the valve motion fail, is to take down the valve gear
parts that would interfere with the moving of the en-
gine, cover the steam ports as described above, and pro-
ceed on one side.
292 MODERN LOCOMOTIVE
THE SOUTHERN VALVE GEAR.
This form of valve gear was invented by Mr. Wil-
liam Sherman Brown, of Knoxville, Tenn., who made
application for a patent on the gear July 11, 191 1, which
was granted to him' July 23, 1912.
The inventor was employed as a locomotive engineer
on the Southern Railway, and the first gear of this type
was used on the Southern Railway Company's locomo-
tive, No. 586, a 22x30-inch consolidated engine, em-
ployed in heavy freight service, which was turned out
m
of the shop at Knoxville, Tenn., in February, 1913.
We understand the new gear proved a success irom
the start, and that the first engine on which it was ap-
plied, with the same gear and set of valves, was still in
service after traveling 150,000 miles, with practically
no expense for work done to the valve parts, which
were replaced identically as they were removed when
the engine was shopped for general repairs.
The fact that the Southern Railway Company has
equipped a large number of their locomotives with this
gear, after giving it a thorough trial in all branches of
the service, is strong evidence of its merits.
Construction.
While this gear is a radical departure from all previ-
ous outside valve gears, it is a gear that can be adapted
VALVES AND VALVE GEARS 293
to any class of locomotive, either inside or outside ad-
mission, and was designed with a view of eliminating
round-house repairs, and delays to power incident
thereto.
In designing the Southern valve gear, the inventor
has eliminated many objectional features that have been
found in other outside valve gears. This gear is very
simple and compact, and contains but few wearing points.
The crosshead connections have been dispensed with,
and the gear has also been correspondingly reduced in
weight.
In Fig. 105 we present the Southern valve gear, show-
ing clearly the construction of the gear and the names
of the parts. This, however, is an earlier type; the
more modern form of the Southern gear is illustrated
in Fig. 106, but the names of the parts are the same
as those shown in Fig. 105.
If the valves are properly adjusted at the time the
engine receives general repairs, the gear is so designed
as to eliminate the necessity of any adjustment in the
blacksmith shop, while the engine is in service. Sim-
plicity of design has long been recognized as one of the
greatest factors in the reduction of maintenance cost
and the elimination of delays and repairs.
Transferring from a rotary to a reciprocating motion
is accomplished by direct movements and on straight
MODERN LOCOMOTIVE
VALVES AND VALVE GEARS 295
lines, thereby doing away with strains and distortions.
The links are horizontal and stationary, which does away
entirely with the wear at this point, as the block only
moves in the link when the reverse lever is moved to
adjust the cut-off, or reverse the gear. The links being
stationary also does away with what is known as the
slip in the link block, found in some outside gears.
There are but eight possible points of wear to the side,
or a total of sixteen wearing points per locomotive, this
being less than half contained in some gears.
Fig. 106 shows a view of the modem gear applied
to a 26x32 Santa Fe type locomotive. It may be seen
that this gear differs in some respects from that illustrated
in Fig. 105.
This gear will practically do away with engine fail-
ures due to breakage of valve gear parts. The different
parts are so balanced as to reduce the wear on the pins
and bushings to a minimum. A 22x30-inch consolidated
engine, equipped with the Southern valve gear in heavy
freight service, after making over 100,000 miles, did
not show any appreciable wear on the pins and bush-
ings; neither had there been one cent spent on repairs
to the valve gear parts. All bearings, pins and bush-
ings of the Southern valve gear are of such size as to
insure long usage with very little wear. The forward
end of the eccentric rod is supported by a bell crank
296
MODERN LOCOU OTIVE
VALVES AND VALVE
298 MODERN LOCOMOTIVE
hanger, which has at its top two bearings spaced widely
apart, thus absolutely preventing any side slap on the
eccentric rod.
Fig. 107 is a kinematic diagram, showing the varying
positions of the different parts of the gear in forward
motion. Starting on forward dead center, or on position
Nos. I — I and C, moving to position Nos. 2 — 2 and C,
bell crank then returning back over position No. i — i to
position Nos. 3 — 3, thence to positions No. 4 — 4, and
then to position Nos. i — i, we follow the diagram of
the gear through the entire stroke.
The Southern gear is designed to eliminate all stress
and strains on reverse lever and reach rod connections,
and the reverse lever is easily handled while working
full head of steam. This feature appeals strongly to
the engineers, enabling them to adjust their cut-off with-
out fear of the lever getting away from them, and will
induce them to work at as short cut-off as possible, re-
sulting in a saving in fuel.
Fig. 108 is a kinematic diagram showing varying
positions in back motion. Starting on forward dead
center, or position Nos. i — i and C, moving to position
Nos. 2 — 2 and C, then bell crank returning back over
position Nos. i — i and C to position Nos. 3 — 3 and C,
thence to position Nos. 4 — 4 and C, from which it moves
to position Nos. i — i and C, the stroke is completed.
VALVES AND VALVE GEARS 299
3()0 MODERN LOCOMOTIVE
Directions for Setting and Adjusting Southern
Valve Gear.
The iiH'tho 1 of setting and adjusting the Southern gear
is clearly exj)laine(l by the following rules, which have
reference to the Southern valve gear layout illustrated
in V\^. T09.
lM*rst. Set the link support so that dimensions con-
form to fit^ures on erecting card. Then connect the
IL^ear as shown on the erecting card.
Second. Set the links so that dimension (M) con-
forms to erecting card.
'I'hird. Set reverse lever in center of quadrant, ad-
just the main reach rod, so that reverse shaft arms will
stand in vertical position.
}^\iurth. Adjust auxiliary reach rods so that link block
will be in center of link when the reverse lever is in
center of quadrant.
Fifth. Set eccentric crank for outside admission to
lead main crank pin, and for mside admission to follow
main crank pin, at a distance from center of main axle
to center of eccentric crank pin to conform to erecting
card.
Sixth. Find dead centers in usual way. With the
engine on front dead center (F), tram from center of
radius hanger pin (P) to any stationary point on cylin-
Valves and valve gears 301
der casing or guide yoke, and scribe arc (a) as shown.
Then place engine on back dead center (B) and again
scribe arc (b) from center (P). If arcs (a and b)
fall line and line, the eccentric crank setting is correct.
If they do not, then knock eccentric crank to or from
center until they do.
Seventh. Then revolve wheel or move engine one
full turn, and tram in same center (P) and scribe arcs
(c and d). In full travel (N) is within 1/16 inch
of eccentric rank circle (O) shown on erecting card
they are correct. If there is a difference of as much
as j4 inch full travel of eccentric crank pin, lengthen
the eccentric crank having the least full travel one-
fourth of the difference, and reset cranks as per para-
graphs 5 and 6.
Eighth. Place engine on front and back dead centers
(F) and (B) and move reverse lever entire sweep of
quadrant. If valves move in same direction as link
block, move link ahead, if in opposite direction move the
link back until still valve is found.
Ninth. To get the length of the valve rod, place en-
gine on front ctead center, allow % inch for lead, or
amount shown on erecting card and adjust valve rod to
lead. (In setting engines on jacks, have the wheels
placed J4 inch under actual running height; for in-
stance, if the blue print running height is 18 inches
302
MODERN LOCOMOTIVE
o
l-H
v8
VALVES AND VALVE GEARS 303
when the engine is on the rail, set the main wheels at
17^ inches running height on jacks.) Then try for
full valve travel in forward position on each side of
engine. If the valve travel is found to be unequal make
necessary corrections by lengthening or shortening the
auxiliary reach rods. For example, say 6 inches is the
desired valve travel, lengthen the auxiliary reach rod
on left side until 6-inch travel is obtained. Then pro-
ceed to run cut off in full gear, and if necessary lengthen
or shorten valve rod to equalize cut off. Then run cut
off at about 9-inch piston travel and equalize same.
Tenth. Raising or lowering the links, by means of
liners, has the same effect as shortening or lengthening
valve rods, therefore any derangement which may occur
can be corrected without disconnecting any part of the
gear.
Breakdowns.
First. If the eccentric crank or eccentric rods fail,
disconnect the eccentric rod from the crank, radius
hanger and transmission yoke, tie up the hanger and
the yoke, clamp the valve in its central position, and
proceed.
Second, If the radius hanger fails, disconnect the
hanger from the rod and take down the eccentric rod.
Then clamp the valve in its central position, and the
locomotive is ready to proceed.
304 MODERN LOCOMOTIVE
Third. In the event of the transmission yoke failing,
disconnect it from the eccentric rod. Then proceed, first
clamping the valve in its central position.
Fourth. When the horizontal arm of the bell crank
fails, disconnect the yoke from the eccentric rod, tie up
to clear, clamp the valve centrally, and proceed.
Fifth. If the vertical arm to the bell crank fails, or
breaks, clamp the valve in its central position and pro-
ceed. It will sometimes be found necessary, however,
to take down the broken vertical arm.
Sixth. In case of the failure of one auxiliary reach
rod, or the reverse shaft arm, block both link blocks in the
same position in the links, and in such a position as to
give sufficient port opening to start the train and to con-
trol its speed by the throttle.
Seventh. If the main reach rod, or the middle arm
to the reverse shaft, fails, or if both auxiliary reach rods
fail, block the link blocks same as in case of one broken
auxiliary reach rod, or reverse shaft arm. The power
and speed of the locomotive may then be controlled by
the throttle.
Laying Out the Southern Valve Gear.
By J. B. Gwin, Chief Draftsman of the Southern Loco-
motive Valve Gear Co., Knoxville, Tenn.
Lay oflF the diagram on scale of half size, as follows :
Lay off the center line through the center of the drivers.
VALVES AND VALVE GEARS 305
Fig. Ill, and cut this line with a vertical through the cen-
ter of the main axle at A. From center A, lay off both
main pin circle, and eccentric pin circle, d — d and e — e re-
spectively. Now locate the center of cylinder; then,
with tram set to the length of the main rod, locate the
center of the crosshead pin on the center line of the
cylinder at i, from forward dead center. Now, with a
straight edge through centers A and i, draw the center
line of the main rod. This is done in order to get the
exact position of the main pin center above the center
line of the drivers, which is very necessary for obtaining
the length of the eccentric crank. Next, locate the bell
crank center T to suit the available horizontal distance
from the center of the main driver, and the vertical
height above the center line of the drivers, if possible,
so that the piii in the vertical bell crank arm will stand
Yz inch below the center line of the valve stem, with the
pin in its lowest position. Then, with radius equal to the
length of the bell crank arms, from bell crank center T
scribe arc Tj. Next drop a vertical from a point Tg, in
Fig. no. Then the length L measured on diagram,
Fig. no, will be the approximate length of the eccentric
rod.
Now calculate the ratio of the long and short end of the
eccentric rod, using diagram formula. Fig. no. Set the
tram to the equal length of the long end of the eccentric
3o6
MODERN LOCOMOTIVE
l-H
VALVES AND VALVE GEARS 307
rcxi, and lay off arcs b — ^b, from centers B and Bi, inter-
secting at E, the center of the lower radius hanger pin
when the engine is standing on either dead center.
Now, with the same tram, lay off arcs ba — bg, from
centers C and D ; then set the tram to the total length L
of the eccentric rod, and lay off the arcs f and fi, and
the arcs Q and Cj, from the centers B and B^, and C
and D, to the extreme forward centers of the lower
transmission yoke pin centers F, Fj, Fj, F,, F^, and F5.
Now set the tram to the length equaling the height of
bell crank center T above center line of drivers, plus i}i
inches; this will be the suitable length of the radius
hanger. For example, say that the height is 33^^ inches,
plus ifi inches, which would equal 34J4 inches, the
length of the radius hanger. Now strike the arc G, from
the center E; arc G will be the radial center, and the
intersection of the arc G and the heavy line Ji will
be the vertical center, of link and radius hanger. Now
lay off the centers H and I. This distance will have
to be found by trial, in order to obtain the proper valve
travel. I is the link block center position, forward mo-
tion, and H is the same, for back motion. Take the tram
with length equal to the radius hanger, and, from center
I strike the arc J, also from center H, strike arc K. Now
lay off the eccentric rod center lines as follows: Lay
off the center a, cutting centers B and E, and arc f at F.
3o8 MODERN LOCOliOnVR
This for inside admission valves, and a^ for outside ad-
mission valves, cutting centers B^ and E, and arc f^ at
F,. Lay off aj, cutting center A and arcs b, and Q, and
J at L and Fo. Lay off a,, cutting center A and arcs b,
and o,, and K at O and F3. Lay off a^, cutting center A
and arcs bg and Q, and K at N and F4. Lay off center
a^, cutting center A and arcs b^ and C,, and J at M
and F5.
Now set tram to a trial length for the transmission
yoke, say about y/[ inches shorter than the radius hanger.
From center Fo, scribe the arc 1, cutting the arc T^. And
from the center F^, scribe the arc m cutting the arc T^.
Now from the centers Fa and F^, scribe the arcs n and
o, cutting the arc T^.
Now, if the arcs 1, m, n, and o intersect exactly on the
arc Tj, this shows that the eccentric rod and transmis-
sion yoke are of proper length. But if the arcs 1 and m
intersect on the arc T,, and the arcs n and o intersect on
the outside of arc T^, the transmission yoke needs to be
lengthened.
If the arcs n and o intersect on the arc Tj, and 1 and
m on the outside, the transmission yoke needs to be
shortened. But, if all four arcs 1, m, n, and o intersect
an equal amount outside of the arc T^, the eccentric rod
needs to be lengthened, while, if all four arcs intersect
inside of the arc T^, the eccentric rod must be shortened.
VALVES AND VALVE GEARS 309
It is needless to say that any change in the length of
the eccentric rod will call for a revised calculation for
the lap and lead ratio, by the diagram formula, Fig.
no.
For inside admission, the main pin leads the eccentric
crank pin, and with outside admission, the main pin fol-
lows the eccentric crank pin. The full black lines of the
eccentric crank and rod are for inside admission, and
the broken lines of the eccentric crank and rod are for
outside admission.
THE YOUNG VALVE GEAR.
A new design of radial outside valve gear, designed
to take care of the large cylinder volumes now being
used, which is reallv a modification of the Walschaert
valve gear, end somewhat resem.bles the Lewis valve
gear which was used on a few roads between 1892 and
1895, was patented September 2, 1913, by Mr. Otis W.
Young, of Chicago, III.
The valve gear was designed to give better and more
economical steam distribution, with increased valve
travel, than is possible to obtain with the use of the
Walschaert valve gear. But with the same travel, lap,
lead and clearance as the Walschaert valve gear, the
Young gear gives no better events than the Walschaert
type.
3IO MODERN LOCOMOTIVE
Within the limit of 6j^ inches valve travel, the Wals-
chaert valve gear performs satisfactory service, but with
7 inch travel or more, common to the larger and more
modern locomotives, very objectionable angularities arise.
These are eliminated by the use of the Young valve
gear, which gives satisfactory results with a valve travel
up to 8y2 inches. The object of greater valve travel
than has heretofore been practicable is to increase the
lap and lead and consequently provide wider port open-
ings needed for handling large cylinder volumes.
The equipment is very simple in construction, em-
bodying rigid bearings, and straight thrusts without ob-
jectional angularities. The entire arrangement is well
standardized, so that new parts are easily obtainable.
and GonstructioiL
The Young design is an entirely new form of radial
type of outside valve gear. Its simplicity of design and
construction is due to the embodiment of the fewest
possible working parts.
The motion of this valve gear, as may be seen from
the illustrations, Figs. 112 and 113, is derived entirely
from the piston and crosshead connections, thereby
eliminating distortions resulting from the slip of the
driving boxes, wear of journals brasses, and settling of
the equipment upon its springs. The 90 degree move-
ment of the main travel is obtained by a pair of con*
VALVES AND VALVE GEARS 3II
centrically mounted rockers. These rockers transmit the
variable component of the motion from the crosshead
and link on one side to the lap and lead lever on the
other side. A reduction in the size of the block and the
link is made possible by constructing the link with in-
tegral .trunnions, thus obtaining a reduction of 40 per
cent in reciprocating weight, without sacrifice to wear-
ing surfaces. Fig. 112 shows the Young valve gear,
with the steam chest cut away to show the Young piston
valve in operation.
Each piston, in operation, causes valve movement equal
to the lap and lead on its own side and travel on the
opposite side. The valve is moved a distance equal
to its lap and lead each way from its central position by
the movement of the piston through an entire stroke,
when the radius bars are both central in the link. In
this valve gear the source of motion is the piston alone,
and the right engine is 90 degrees ahead of the left;
while the left engine is 270 degrees ahead of the right,
therefore the valve travel producing members must be
direct on one side and indirect on the other. Thus, for
forward motion the back end of the right radius bar is
above the center of oscillation of the link and the left
radius bar below. The reverse is true for backward mo-
tion. The various cut-offs are obtained with the radius
bar in intervening positions between its central and ex-
VALVES AND VALVE GEARS 313
treme locations. Valve travel in addition to lap and lead
is produced through the oscillation of the link which
causes the radius bar to oscillate the rock shafts. This
motion is effective on the valves* on the side of the loco-
motive opposite to the link imparting motion. As the
front end of the radius bar acts on the lap and lead lever
between its two extreme connections, unusually long
travel is imparted to the valve without excessive link
angularities. As the movement of the links is constant
under all operating conditions this is desirable.
Valve Setting.
In locomotives using valve gears that derive a portion
of their movement from a connection to the driving
wheels, as, for instance, the Walschaert, it is necessary
to take wheel centers before proceeding to set the
valves — this is essential for the reason that only by
knowing the correct wheel centers, is it possible to deter-
mine whether adjustment is needed in the eccentric
crank or in the eccentric rod.
With the Young valve gear, which has no connection
to the driving wheels, the method of taking wheel cen-
ters may be simplified. It can, and, in fact, is, pre-de-
termined on the drawing board, by the following process.
The length of the main rod, and the piston stroke, are
known in every valve application, and it is only a mat-
ter of laying down a few lines on paper to determine
314
MODERN LOCOMOTIVE
VALVES AND VALVE GEARS 315
how far back of its central position oi>e crosshead must
stand, due to the angularity of the main rod, when the
other crosshead is at its extreme travel, which position
it must occupy when the wheel is at its dead center. All
erecting cards showing the assembled Young valve gear
are arranged, therefore, to show the exact distance back
of its central position that one crosshead will occupy,
when the wheels on the opposite side are on their true
centers. This distance varies in different designs of
locomotives if the main rod lengths and piston stroke
vary, consequently it must be obtained from the blue-
print for the class of locomotives on which the Young
gear is to be set.
For these reasons it is not necessary, in setting the
Young gear, to take wheel centers in the shop, or even
to have the wheels under the engine, nor is it necessary
that the main rods be connected ; in fact, it is better not
to have the main rods up.
With the above thoroughly understood, the valves may
be set as follows:
. With crossheads connected to pistons, the main rods
disconnected, mark the piston striking points on the
guides.
Show a mark on the guides central between the strik-
ing points, place the crossheads back of this central
mark the distance designated on the erecting card.
3l6 MODERN LOCOMOTIVE
If the radius bar can then be moved from its lowest
to its highest positions, without movement of the valves,
the dimension on the union link is correct. If not,
shorten or lengthen the union link to suit.
With one crosshead in the above position, move the
opposite crosshead to each end of its stroke, and equalize
the lead to show the same opening for front and back
ports, by means of the nuts on the valve stem.
Repeat the process on the opposite side. Then adjust
the main rod lengths to obtain equal piston clearance in
both ends of the cylinder.
The valves will then be perfectly square, without re-
sorting to rollers for checking the cut-off.
Breakdowns.
Because of its simplicity of construction and oper-
ation, and its rigid bearings, the Young valve gear is
much less liable to breakdowns than is the Walschaert
gear. An objection is often made, that in the event of
a break down on the road, a locomotive equipped with
the Young gear is unable to proceed after one side is
disconnected. This is true to a certain extent, but it
must be remembered that cases are few where modem
large locomotives have actually been brought in under
their own power after disconnecting one main rod ; there-
fore the Young valve gear is as efficient in this respect
VALVES AND VALVE GEARS 3 17
as the other forms of valve gear in use today. In fact,
one valve may be disconnected, and the ports covered,
and as long as both main rods are up, the Young gear
will continue to operate. To meet this objection, how-
ever, an arrangement may be provided wherein the union
link connects the reversing link to the main pin instead
of to the wrist pin. This arrangement has an advantage
over other valve gears inasmuch as it eliminates the use
of an eccentric crank. It provides the same valve mo-
tion as the connection to the wrist pin, but is not, how-
ever, the preferred method.
This valve gear is manufactured by the Pyle-National
Company, of Qiicago, 111.
THE END.
Absolute pressure, 2,*j
Accidents to locomotives, 252, 289, 303, 316
Adjusting the valve, (See Valve Setting.)
Admission, 8, 58, 93, 97
commences, 58
Duration of 58
Inside 8
Outside 8
Point of 8
port, 8
Pre- 8, 70, 73
valve, 9
Double 124, 161
Advance, Angle of 9, 90
Linear 22, 90
of eccentric, 15, 92, 94
Allen slide valve, 123
-Richardson balanced valve, 137
Allfree piston valve, 174
cylinders, 173
American balanced valve, 138
semi-plug piston valve, 178
Angle of advance, (.See Advance)
lead, (See Lead)
Angular advance of eccentric, 15, 92, 94
Angularity of connecting rod, ^^
320 INDEX
Area, Balanced 132, 136
Piston 25
Port 41, 43, 44, 45
Steam port 43, 44, 45, 46
Arm, Crank 13, 83
Eccentric 15
Rocker 30
B.
Back pressure, , 27, 68
Backward eccentric, 16
gear, Full 19
Baker valve gear 275
Accidents to 289
Application of 280
description, 278
History of the 275
parts, 277
setting, 283
Balanced area, 132, 136
valve, 9, 130
advantages, 134
Allen-Richardson 137
American 138
disadvantages, 134
Gould 141
History of the 130
Hole in top of the 133
Mewes 144
Miller double acting 156
Richardson 135
INDEX 321
Balanced valve, versus piston valve 186
Walsh 159
Wilson 161
Balancing a valve, 131
Advantages and disadvantages of 134
Methods of ,. . 133
Object of 131
Over 136
Bell crank, 10
Bar, Radius 28
Rocker 30
Transmission 30
Block, Link 22
Valve 31
Boiler pressure, 27
Box, Rocker 30
Stuffing 30
Breakdowns, 252, 289, 303, 316
Bridges, 40
Construction of 40
Valve seat 31, 40
C.
Carrier, Link 22
Cavity, Exhaust 17, 38
Center, 10
Dead 10
Line of : . 10
line of motion, 24
Chest, Universal valve 191
Valve 31
322 INDEX
Circle, Crank pin 86
Clearance lo, 57, 67, 68
Amount of 56
Effect of 55, 68
Kxhaust II, 55, 56, 57
Inside n, 55, 56, 57
Outside II
Piston II, 68
Combination lever, ii, 238
Compression, ii, 60, 62, 95
Advantages and disadvantages of 63
commences, 63
Duration of 63
Kffect of 62, 70
Point of 12
Conncctini^^ rod 12, 'jy
Angularity of 'JJ
Connector, I^p and lead (See Union Link.)
Constant lead, 21, 73, 212
Crank, 12, 84
arm, 13, 83
Bell 10
circle, 86
Eccentric 13, 86, 249
end, 13
Leading 13
motion, 13
pin and piston. Relative position of 'JJ
throw, 13
web, 13
wrist, 14
INDEX 323
Crosshead, 14
guides, 14
Cut-off, 14, 58, 94
Determining point of 14, 59, 61, loi, 104, 106
Effect of 59
early 60
Lap will effect the point of 59
Lead will effect the point of 104
Point of 14, 59, 61, 104, 106
Short 14
Travel will affect the point of 60, 107
valve, (See Expansion Valve.)
Cylinder, Allfree piston valve 174
Piston valve ~ 173
Sheedy's outside steam pipe for old 197
D.
Davis variable lead attachment, 270
D-slide valve, , 35, 36
Dead center, 10
Direct valve motion, 24, 100, loi
distinguished from indirect motion, loi
Displacement, Piston 26
Valve 31
Distribution of steam, Events in the 113
Double admission valve, 124, 161
exhaust valve, 161
Duration of admission, 58
compression, 63
exhaust, or release, 64, 96
expansion, 61
^ead, 70, 74
preadmission, 74
324 INDEX
E.
Eccentric, 15, 83, 85
Adjustable 15
Angular advance of the 15, 92, 94
arm, I5» 85
Backward : 16
crank, 13, 86, 249, 284
Eccentricity of the i7, 86
Exhaust 16
gear, 16
position for a valve without lap, 87
with lap, 90
radius, 86
Relation between the valve and the 82
rod, 16, yy, 287
connection to link, 244
length, 243, 285
sheave, 16, 85
strap, , 85
throw, 16, 86, 243
Virtual 236
Eccentricity, .> 17
of the eccentric 86
Effective pressure, 27
Mean ■ 27
Equal lead, 21
Events in the distribution of steam, i. . 113
Exhaust, 17, 63
cavity, , .17, 38
commences, 64
clearance, (See Clearance.)
INDEX 325
Exhaust, Duration of 64
eccentric, 16
lap, 17, 19
Negative 20
lead, 17, 21
nozzle, 17
port, 17, 38, 46, 47
width, 46, 47
Point of 18, 63, 64
Expansion, 18, 61
Duration of 61
Initial 18
valve, 18, 58
Variable 18
F.
Face, Valve 32, 48
Foot, Link 22
Forward gear, Full 19
Fulcrum, Link 242
G.
Gab hooks, 203
Gear, , (See Valve Gear.)
Eccentric 16
Full , 19
backward 19
forward 19
Gould balanced valve, 141
Guides, Crosshead 14
Valve stem 33, 250
326 INDEX
H.
Hanger, Link 22
Head, Piston 26
High pressure, 27
History of Baker valve gear, 275
balanced valves, 130
D-slide valve, 35
piston valves, 166
Southern valve gear, 292
Walschaert valve gear, 205
Young valve gear, 309
Hole in top of balanced valves, 133
Hook motion, 203
I.
Indirect valve motion, 25, 100
distinguished from direct motion, 101
Initial expansion, '. . . . 18
pressure, 27
Inside admission, 8
clearance, ", 55» 5^, 57
lap, 20, 54, 55
K.
Kingan-Ripkin valve gear device, 266
L.
Lap, 19, 91
Amount of 19, 234
and lead lever, (See Combination lever.)
changes the point of cut-off, 59
Eccentric position for a valve without ' 87
with 90
INDEX 327
Lap, Effect of 19
inside 54
outside 53
Exhaust 17, 19
Inside 20, 54, 55
Negative , 20
of slide valve, Problems relating to the loi
Outside 20
Seal (See Seal.)
Steam 20
Valve with 5^, 53» 54
without 51, 52
Lap and lead lever, (See Combination lever.)
Lateral motion, 25
Lead, 20, 69
Advantages of 70, 72
affects the point of cut-off, 104
Allen valve 126
Amount of 70, 71
angle, 21, 91, 94
attachment, Davis' variable 270
commences, .70, 71
Constant 21, 73, 212
Equal 21
Exhaust 17, 2X
Inside 55
Negative 21, 71
opening, 70, 7^' 93
Point of 70, 93
Positive 21, 71
328 INDEX
Lead, Preadmission a result of 70
Steam 21
Variable 21, 213, 247, 265, 270, 288
Leading crank, 13
Length of eccentric rod, 243
radius rod, 242
Lever, Combination 11, 238
Lap and lead (See Combination lever.)
Reverse 29
Lift shaft location, 245
Line of center, 10
motion. Center 24
Line and line, Valve 32
Linear advance, 22, 90
Link, 22
block, 22
movement, 243
carrier, 22
Eccentric rod connection to 244
foot, 22
fulcrum, 242
hanger, 22
Main 22
motion, 22
Oscillating (See OscillatingTT'
radius, 23
Reverse 29
saddle, 23
stud, 23
shaft, 249
Slip of the 23
INDEX 329
Link, slot, 23
radius, 242
stirrup, (See Link-carrier.)
swing, 23, 243
Union 24
Linking-up, 24
Lost motion, 24> 73
Low pressure, 27
M.
Main link, 22
pin, 24
rod, 24
Mean pressure, 28
Mewes balanced valve, 144
Mid-position of valve, 32
Miller slide valve, 127
double acting balanced valve, 156
Motion, 24
Center line of 24
Crank 13
Direct 24, 100, loi
distinguished from indirect loi
Hook 203
Indirect 25, 100, 101
Lateral 25
Link 22
Lost 24, 73
Reciprocating 25
Reverse 29
rod, 25
Valve 25
330 INDEX
N.
Negative exhaust lap, 20
lead, 21
Nozzle, Exhaust 17
O.
Obliquity of connecting rod, .... (See Angularity, etc.)
Opening, Exhaust 64
Lead 70, 71, 93
Port 26, 40
Outside admission 8
clearance 11
lap, 20
steam pipe for piston valves, Sheedy's.... 197
Overbalancing, ; 136
Over travel 25, 66, 67
Oscillating, 25
P.
Pin, Main 24
Relative position of piston and crank yy
Saddle 30
Piston area, 25
clearance, ii, 68
displacement, 26
head, 26
rod, 26
Relative positions of crank pin and. jy
valve and 93
stroke, 26
travel, (See Piston stroke.)
valve, 26, 166
IND2X 33^
Piston valve, Advantages and disadvantages of the.i86, i88
Allfree 174
American semi-plug 178
arrangement, Straightway 194
Built up type of 168
cylinder, Allfree 173
Design of 168
General design of 168
History of the 166
Operation of the 170
Sheedy's outside steam pipe for 197
Size of 169
Solid type of 169
Straightway 194
versus balanced slide valve, 186
Young 184
Plate, Pressure 28
Valve 32
Point of admission, 8
compression, 12
cut-off, 14, 59, 61, loi, 107
exhaust, 18, 63
lead opening, 70, 93
release, 29, 63
Port, 32, 38
Admission 8
area, 41
Exhaust 17, 38, 46, 47
Location of 37, 38, 42
opening, 26, 40, 41
Valve 33, 40, 41
332 INDEX
Port, Steam 38, 42
Width of the .' 46
Positive lead, 21
Pow«r required to move a valve, 128
Preadmission (See Admission.)
distinguished from lead, 70
Duration of 74
Pressure, Absolute 27
Back 27, 68
Boiler 27
Effective 27
High 27
Initial 27
Low 27
Mean 28
plate, 28
Terminal 28
Q.
Quadrant, 28
R.
Radius bar, 28
Eccentric 86
Link 23
slot 242
rod. Length of 242
Reach rod, 28
Reciprocating motion, 25
Release, 29, 63, 96
commences, 64
Duration of ^ 96
Point of 29, 63, 64
INDEX 333
Reverse, 29
lever, • . . . . 29
link, 29
motion, 29
shaft, 29, 249
valve. 29
yoke, 30
Richardson balanced slide valve, 135, 137
Rocker arm, 30> 97
bar, 30
box, 30
Valve with 98
without 97
Rod, Connecting 12, j*j
Eccentric 16, *JT, 287
Length of radius 242
Main 24
Motion 25
Obliquity of connecting (See Angularity.)
Piston 26
Radius \.. 28
Reach 28
Valve 33, 287
S.
Saddle, Link 23
pin, ^ 30
Seal, 30
Seat, Valve ; 37, 39
Sector, Valve (See Quadrant.)
Semi-plug piston valve, American 178
Setting the valves, 260, 283, 300, 313
334 INDEX
Shaft, Lift 24s
Link 249
Reverse 29, 249
Tumbling 31
Sheave, l^ccentric 16, 85
Sheedy's outside steam pipe for piston valves 197
Short cut-ofF 14
Slide valve 33, 35
advantages and disadvantages, .... 188, 189
Allen 123
invention 35, 36
Miller 127
Slip of the link 23
Slot, Link 23
Southern valve gear, 292
Accidents to ■ 303
breakdowns, .... (See Accidents.)
construction, 292
diagrams, 296, 297, 299
History of the 292
Laying out the 304
parts, 294
setting, 300
Spindle, Valve 33
Steam distribution, 113
lap, 20
lead, 21
pipe, Sheedy's outside 197
port, 38, 42, 43, 44, 45, 46
area, 43, 44, 45, 46
Stem, Valve 33
mi>M 335
Stirrup, Link (See link Cafrieri)
Straightway piston valve arrangement, 194
Strap, Eccentric v, •:?.■. • 85
Strip, Valve i • . . . 34
Stroke, Piston 26
. Valve (See Valve Stroke.)
Stuffing box, ; „ .**>.. . 30
Swing of link, , ..... .23, 243
> • <
T.
Terminal pressure, .1. ... . 28
Throw, Crank i ........;.. . 13
Eccentric 1 . . . 16
pin 243
Virtual eccentric 236
Transmission bar, 30
Travel of piston, (See Piston Stroke.)
valve, 34, 65, 86, 286
Over .25,-65, 66, 67
will affect the point of cut-qff .60, 107
Tumbling shaft, r . . . .r. . • . 31
U.
Union link, 24
Universal valve chest, 191
V.
Valve,.Admission ; 9, S^
Allen slide ; 123
-Richardson balanced 137
Allfree piston 174
American balanced 138
semi-plug piston. .•..•.•..«..». 178
336 INDEX
Valve, Balanced (See Balanced valves.)
block, 31
bridge, 31, 40
bushing, 31
chest, 31
Universal 191
clearance, (See Clearance.)
construction, 48, 49, 50
Cut-off (See Expansion valve.)
cylinder, AUfree's piston 173
D-sHde 35, 36
displacement, 31
Double admission 124
exhaust 161
Expansion 18, 58
face, 32, 48
functions, 36, 37
gear, (See Valve gears.)
Gould balanced 141
Hole in top of balanced 133
History of the D-slide 35
Linear advance of 22, 90
line and line, 32
Mewes balanced 144
Mid-position of 32
Miller double acting balanced 156
slide 127
motion, 25
Direct 24, 99, 100, loi
Indirect 99, 100, loi
Over travel of 66, 67
INDEX 337
Valve, Piston (See Piston Valves.)
plate, 32
port, 32, 37, 38
opening, 33, 40, 41
Power required to move a 128
Problems relating to lap of the slide loi
Relation between the eccentric and 82
piston and 93
Reverse ' 29
Richardson balanced 135
rod, 33, 287
seal, (See Seal.)
seat, 37, 38, 39
bridges, 31, 40
Construction of 37> 38, 39
False 39
Width of 39
sector, (See Quadrant )
setting, 260, 283, 300, 313
Slide 33, 35
stem, 33
guide, 33, 250
spindle, 33
strip, 34
travel, 34, 65, 86, 286
Walsh balanced 159
Wilson's balanced slide 161
with lap, 52, 53, 54
Position of eccentric for a 90
rocker, 97
3,^8 INDKX
/ 'iihc, without lap 51, 52
Position of eccentric for a 87
rocker, 97
yoke, 34
Yoiingf piston 184
\'alve-gear 19, 32, 202
Accidents to 252, 289, 303, 316
liaker 275
breakdowns, 252, 289, 303, 3ir»
device, Kinfjan-Ripken 266
Southern 292
W'alschaert 205
Voting 309
Variable expansion 18
lead 21, 213, 247, 265, 288
allachment, Davis 270
Virtual eccentric tlirow, 236
W.
Walscliaert, K<f'u\c 205
valve i^vixr 205
Accidents to 252
Adjustine: the 260
analysis 210
arrangement, 230
breakdowns (See Accidents.)
construction, 214
History of the 206
parts, 231
setting 260
Walsh balanced slide valve 159
INDEX .^9
Web, Crank 13
Wilson balanced slide valve, 161
Wiredraw, 34, 75, 76
Wrist, Crank 14
Y.
Yoke, Reverse 30
Valve 34
Young piston valve, 184
valve gear, 309
Accidents to 316
breakdowns, (See Accidents.)
construction and design, 310
setting, 313
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